When replying to mail (especially on mailing lists, but equally true elsewhere), please cut out the signature of the person who's mail you're replying to. It's unnecessary information and just wastes bandwidth and my time in looking for the useful content.
Also, signatures are supposed to be about 4 lines, max. 5 or 6 doesn't tend to bother me, but 12 does.
Oh, and while I'm ranting about mail — replies go below the original text. The original message provides necessary context for the reply. By replying at the top of the mail, I have to scroll down, read the context, and then go read what's at the top again. Snip unnecessary stuff when replying as well. I tend to actually reformat mail that I reply to if the reply was at the top, but it's too much trouble when you're replying late in a thread.
There, I feel better now. 🙂