Reacher: Essentially it works in the same way as your traditional 5 bladder pneumatic suit. The difference is that the liquid is there the whole time, but more spread out. When you pull g the liquid is forced into parts of the suit that are designed to put pressure on your lower extremities, trapping the blood in your upper body (by preventing venous pooling). The challenge is to design a suit that does this without massive quantities of liquid, thus making it prohibitively heavy. This is where the germans have succeeded by using a liquid designed for the task (we suspect some kind of weak beer...)
BOAC: A standard 5-bladder anti g suit as used by majority of the RAF FJ community does indeed "add" 1 to 1.5 g onto your basic g tolerance. However, it tends to have a slightly better effect than this, as it "reminds" you to strain, even for lower g antics where you might get caught out on a bad day(around the 4 g mark). In addition it gives you something to strain against, rather than having to artificially tense your muscles, which is hard to do effectively. However, as you said, it's primary effect is to reduce fatigue when exposed to high g for long periods. However, more modern equipment (combat EDGE and the typhoon g-suit/vest) add considerably more to ones basic g tolerance. Typhoon in the UK has full coverage anti-g trousers, pressure breathing combined with a pressure vest, which allows a (nearly!) relaxed 9g, so very effective. Had the pleasure of seeing it in action in the centrifuge and it's great to watch. (Although apparently makes your feet hurt like hell!)