I don't buy music very often, and when I do I rarely take risks on new artists. I like to spend my money wisely when it comes to music. I'm more likely to buy an album from an artist I'm familiar with.
CNET music downloads is great because there are plenty of larger named artists that will offer one or two tracks for free so you can sample their new releases. It's also a great way to explore music you've never heard of because the site offers hundreds of thousands of free full tracks posted by the artists.
Personally, I love listenting to smaller, independent artists. Often, you can find a rare gem nobody else knows about. CNET has lots of independent music available. These artists sometimes offer full downloads of at least one of their albums so you can become familiar with them.
I'm also curious about different genres and subgenres of music. CNET neatly organizes all the mp3's into at least a hundred subgenres. Many of them I've never heard of before visiting the site. This has been broadening my knowledge of music considerable. I'm listening to a lot more music than usual, and next time I buy an album I have a pretty good idea what albums it will be.
If you find an artist you like -- be sure to support them by buying their CD.