I've returned 2 phones because of this....phone 1: had for around a year-ish (Feb/Mar '10 - Feb / Mar '11) ... Phone 2 (100% stock), lasted until about early / mid May. Same issue: freaking out like it was possessed.
My two cents: DEFINITELY hardware issue. Why? Well, after trying to get into the "privacy" area to do a factory reset thru there for about 10-20min, I got very ticked off. Like any true IT person, I took the device, slammed it face-down a couple times on the table, and low n behold, the buttons / screen responded to my touch - albeit it still fought me.
So there's my reasoning that it's a hardware issue - nothing to do with charging or condensation. (background: I would actually leave it sitting on the table all day - normal temp (68-ish?) / humidity ... also it would still spazz out when the keyboard was slid out). Oh, btw, the reason I tried to do a factory reset via "Privacy" is because I couldn't any other way - the VZW rep couldn't either...after playing with it for 5-10min he was ready to give up, as he couldn't even get passed the slider screen (you couldn't just touch n slide...you had to slap n slide..lol)
okay...my two cents...
If you have insurance, bring it in, show a rep what's up...make sure you're not rooted, etc.. as they ARE QUICK to blame it on a software issue - even tho the issue still persists after rebooting.
I wish i had seen this post the last two times I went in. I would have printed it and brought it with me.