I'll second what Deb said about chain wear. By the time I noticed I needed a new chain, I needed a new cassette as well.

I'm curious about the tires though. I noted that you said that your friend looked at your tires. Hard to imagine that young tires with less than 2000 miles would look particularly bad. Hoping I don't jinx myself but one of the tires on one of my bikes is over 4 years old, 4000+ miles and looks mine to me!