A perennial topic of discussion on Lonely Planet's Thorn Tree is the availability, or non-availability, of ferry service between Fujian's mainland and Jinmen (Kinmen) island - a small piece of Fujian Province of China - which is actually controlled by the Republic of China (Taiwan). Here's a current update, as of February 2012.
The terminal in Shijing
I was riding from Quanzhou to Xiamen, and the idea of taking the ferry from Shijing Town (石井镇) (near Quanzhou) to Jinmen, and then from Jinmen to Xiamen, was certainly appealing, as the ferries would eliminate some of the comparatively boring overland travel in this area. There is indeed a large ferry terminal in Shijing, and there are indeed ferries to Jinmen there. The first ferry leaves the mainland at 8:30 (you probably will want to be at the ferry at least 30 min in advance), and there are probably a couple more of them during the days, judging by the schedule I later saw in Jinmen. (There did not seem to be a schedule prominently posted in Shijing).
Shijing, in a sense, is wonderfully set up as a departure point: you can get there after an afternoon of sightseeing at the famous ancient Anping Bridge a few miles to the north (between Anhai 安海 and Shuitou 水头 towns; you really want to walk the entire length of the bridge, if you can!), and spend the night in town waiting for the morning ferry. The ride or drive from Shuitou to Shijing, along the new riverside road is quite pleasant; there is little traffic now, but there is apparently a lot of new development going on, mostly connected with the cross-straits trade.
While the quayside hotels in Shijing are on the luxury side (lots of "karaoke" places, according to signs), there are decent budget options in a quiet street just a block or two inland - in one of them, I had quite a decent room for just Y60. (In contrast, in Xiamen, I think, it's a much longer distance from either the Dongdu or Wutong ferry terminal to any of the budger hotel districts). Plenty of food choices too.
There is only one problem with the Shijing ferry: the Shijing to Jinmen ferry presently does NOT carry thrid-party natioinals (i.e., those not with a PRC or ROC passport). First I did not entirely believe that I had understood the ticket clerk's words correctly, but I checked with a uniformed immigration official, and she confirmed the situation. So for most of us foreign travelers this is not an option, but stay tuned... things may change - and I hope they will!
Inside the Dongdu Ferry Terminal (aka International Cruise Terminal), Xiamen
The second attempt, at Dongdu terminal (just north of downtown Xiamen), a couple days later, carried no surprises. Ferry service is pretty frequent (pretty much hourly all day, until 5 pm or thereabout), the ticket cost (the fare _+ mandatory "service charge") was Y150, facilities decent, and check-in smooth and quick. Sort of like going through an international airport, but without all the time-costly hassles that an airport involves.
On the Marco Polo
For obvious reasons, no national flags seem to be flown on the ferries.
There are both Xiamen-based and Jinmen-based ferries on this route, operating in a more or less alternating order. The Xiamen boat, the Marco Polo was certainly an "atmospheric" old vessel, passengers grabbing on railings and ropes as the little craft pitched, rolled, and yawed on its way between the two islands. The views are great... except that it's usually pretty foggy in Xiamen's waters, and in February it's still fairly cold, even though we're just a degree north of the Tropic of Cancer.
"Three People's Principles for One China". The first R.O.C. fortification.
After about an hour, a small island with a little fortification decorated with a 三民主义 （Three People's Principles of Sun Yat-sen) appeared, and perhaps another half an hour later it was the Shuitou Harbor in Jinmen. This is the harbor where all 3 mainland ferry lines (from Shijing, Dongdu, and Wutong (at the NE corner of Xiamen Island)) terminate. Don't miss the tourist information desk, with all kinds of great free maps - for both Jinmen and the "main island" of Taiwan, hotel information, etc.
At R.O.C. immigration at Jinmen they do ask about your intended destination - you had better put some address on the arrival country in advance. But as I had not bothered doing it, the official was satisfied enough with me putting my (mainland!) cell phone number instead. The customs do have those cute little dogs that sniff at everybody's luggage in search of contraband, fruit, or an occasional ham sandwich.
The next day I went back to Xiamen by a Xiamen-based ferry, the Star of Peace (和平之星)， and the sleek fast new boat made the Marco Polo look like a rustbucket. On this fast new boat, you are not supposed to be outside of the main cabin during the sailing, and the ride was remarkably smooth - almost as if you were still on the terra firma. After a couple cups of tea I looked out and saw an island on the right. "Wonder if it's still the Lesser Jinmen", I thought. But no: there were skyscrapers seen behind it - it already was the Gulangyu!
The boat even had an (entirely empty) first-class cabin, also including small private cabins, on its second floor. I wonder who ever rides there: I did not see any first-class tickets advertised either at the Dongdu terminal or in Shuitou, but I guess the true VIPs don't need to buy tickets in person at the ticket desk...
Re-entering the mainland at Xiamen was as straightforward as as leaving. I may have been the only third-country national on this craft, and, seeing that I am spending too much time filling in my arrival card (figuring the address of my hotel, etc), an official just waived me through without bothering with the minutiae like this.
Taking a bicycle on either ferry was not an issue at all: while I did not see other bikes being carries, the terminal staff and the crew apparently weren't surprised. On both boats, once you are at the dock, or on the boat itself, with the bike, the crew will put it into the luggage area in the back of the boat, where some of the passengers carry quite large items (small cargo, really). There is no extra fee for the bike (or luggage in general). This is certainly a lot more civilized way to travel than by plane, that's for sure.
Schedules (from Jinmen to Xiamen's Dongdu and Wutong, and to Quanzhou). Fares in Taiwanese dollars, but really it's just 750 NT (around $25) all told.
Incidentally, in Jinmen some locals told me that there is apparently also a ferry from Fuzhou (Mawei, to be precise) to the Matsu (Mazu) islands - an even smaller enclave of the R.O.C.'s Province of Fuchien off the coast of P.R.C.'s Province of Fujian. That certainly would have been an even more exotic destination than Kinmen (Jinmen) - but I have no idea about that ferry's details, and in particular its availability to third-country nationals.