Amazing that program icons could cause such an uproar in the community, but not to be left out, I cast my vote:
Thumbs down.
I’ve read the rational behind them and all. I think they are just missing some very fundamental design principles. Something about a picture being worth a thousand words. A two-letter abbreviation is some small fraction of a word. They just don’t scan well for instant recognition. I think the perfect illustration of this is the following link that was posted in a comment on John Nack’s post. It shows a typical desktop – Windows XP – and every five seconds it switches from the old icons to the new ones in the quick launch bar. I think it’s fairly obvious which is the more usable design.
https://www.techwarrior.cx/~roliver/cs3-icons.gif
Just in case the link ever goes down, here are a couple of screenshots comparing the two: