absolutely, I buy heaps of domains when the mood strikes and a lot of them never get developed. I do try to stick something up for each one, it only takes an hour to get a fully automated site setup so that at least its doing something (like a tgp or pic of the day or such).

For the $8/yr it costs to keep them renewed, I think its worth it. Especially when you do get around to doing something with them, you end up having a domain name that gets a little bit of traffic and is already in the search engines, plus domains that are older tend to get better seo positioning too.

cheers,
Luke