Greetings!
My giants are still called "only ones of their kind".
As I mentioned elsewhere, I started generated medium world going to 600 or 700 with lots of civs with a low pop cap and lots of caves (max non-mountain, fewer mountain in the end to reduce rejections). I then started my first human adventurer in the new version (elves were, again, extinct at that point) in 601. I talked throughly to the people in the heavily razed town I started in, so I knew about nearly a dozen caves nearby, most of which were inhabited by DF cockroaches (=giants).
First thing I noticed: This cave density is really cool. You only have to go about 5 paces from one cave to the next, it seems. I can only recommend it. My guess about rejections also seems to be correct: maxing the non-mountain caves does not seem to cause as many rejects as maxing mountain caves, so if you have endless rejects with maxed caves, try reducing the mountain caves first. Also note that caves seem to get generated at the beginning of the recounting of history; if you have maximized cave size, this can make for a hefty delay before the recounting of the history actually begins (huge caves also slow down finalizing sites considerably).
Second thing I noticed: giants really clog the world gen history. After my character met her death at the hands of one of the giants, I checked legends, and sure enough, there were villages having suffered about 2,000 giant attacks already (if numbering is correct, which seems to be the case).
Deathworks