I wear socks... for both the bike and the run. Lin or Defeet or something similar. The socks I like for the tris are a poly mesh, so they air out really, really well. For the sprints, I wear MTB shoes and put em on in transition. This came in BIG handy today, as RIGHT outside the mount line was a pretty nice hill. I passed 5 guys going up that thing, largely due to the fact the I was already clipped in.

No help with the shoes from me, I wear flats. Adidas has a pair of flats out there that are really comfortable and offer a measure of support... and only weigh 5.5 lbs.

i wear socks on the bike and run. i use DeFeet or Ironman. they work nice. as for shoes, racing flats won't have much support as it is. on olympic distance tris, i use the asics gel lytes, they are light and have just enough support. racing flats won't normally have any type of support. sprits. i got a pair of magic racers, wicked light.
marzian

Run only, unless it's cold then I'll wear them to bike as well. I hate cold feet!

I lose time by putting on socks, which is a big factor in the races that I do. But I do it anyway, because otherwise my shoes don't fit properly. I tried going without in my road shoes, and it was quite workable. (It's not actually possible to buy tri shoes that fit me without socks. Curse my shoe size!)
Of course, here are some deterrent pictures from the 2003 Great White North Half-Ironman... no way would I go sockless for that distance.

I always wear socks. Have orthotics I have to wear, so I cannot replace the insole on them as often (do it once a year). Can not stand for them to get all stinky :) Before I wore them (orthotics) I never wore socks tho ....ahhh the good 'ole days.....