Yeah, there's no reason to be malicious, good going for not screwing with him. I think it's astounding how many ppl leave their WAPs open without even realizing it!! But there are freenets all over the place too, which is really cool when you need fast access.
I'd also suggest that, if you want to help the guy out, send him an anonymous email or IM, but it's definitely a good idea to remain anonymous in case a) he freaks out or b) someone else finds his open WAP and does something nasty, then he'll just blame it on you. A text file on his desktop might work too but I'll leave that up to you
