I don't know if this qualifies as a bug but:
Nephilim means "Giant". In their creature file, their [BODY_SIZE] is only 50000, which is 10k less than a Dwarf. So they're not giants, they're actually midgets even by Dwarven standards. So they also die quickly in a higher savagery world.
Also, they don't even live as long as Humans do, having a maximum age of 90. This doesn't jibe with the stories of the ancient, wizened kings from the Bible.
"Nephilim" approximately means "fallen." In some old biblical texts, they are referred to as giants, while others refer to them as apostates or the offspring of angels and humans. While the latter two are less commonly accepted, the inspiration for this race is drawn from those concepts.
However, you are right about them being a bit small. I have beefed them up to 90k (I believe humans are 100k, voidwalkers are 110k, bog trolls are 290k, lizardmen are around 70k and meowkin are very small, around 45k if I recall correctly) and pumped their max age up to 150:190. I should note that the bog trolls are quite challenging compared to vanilla, and you would be wise to have some traps and military ready at the end of the first year. I haven't had a chance to play around with the voidwalkers much, but they won't even bother looking at you until your population and wealth are pretty high (over 100 dwarves, I don't remember the exact number). Nephilim are more of a mid-tier enemy.
On a side note, v0.11 is almost done.
There are a few quite amusing easter eggs that I can't wait for people to discover. Speaking of which, if anyone gets a "mood weapon," I'd love to see some screenshots. So far, I've gotten a trailing skirt artifact (voidwalker clothing), but no new weapons yet, though I barely have any time to play the mod much myself at the moment.
Magma casters and labs are finished, as are new weapons, transmutation, and a few minor quirk/bug fixes (including the bug with shearer/spinner not gaining levels). Transmutation will allow you to take excess plants and perform !!SCIENCE!! on them, possibly creating new and rare seeds not otherwise found in your biome or caravans. As with alchemical experiments, transmutation has some other possible outcomes - some of which are pleasant, some of which are not.
I have added pigeons to the game as common wildlife for your hunters to shoot at. They are small, but easy to kill and plentiful. There is an easter egg related to this creature, but you'll have to stumble across it yourself. It's really amusing - I can't wait to do the graphics for it. Like another easter egg related to walruses (which I don't think anyone but Jeoshua has discovered yet, and he cheated by looking at the raws), this one is highly humorous, but is rare enough that it won't detract from gameplay.
Seeing as there's a high demand for more materials, I'm going to go ahead and push through a new metal. White gold is a crafting alloy, made from one bar of gold and one bar of nickel. It is slightly more valuable than the sum of its parts. While this metal is here to stay, it will be supplemented in v0.12 by some more metals of a more alchemical nature. I have some really interesting plans for this concept, so stay tuned. I am also adding a new gemstone to mithril veins/clusters - but be aware that this gem is quite rare.
All I've got left to do besides that is a few spoiler-related graphics, and the graphics for a new megabeast - the manticore.