I've had my iPod jailbroken for about a month now, and I think Cydia is a great resource for apps and themes. I love the fact that I can have my weather on my lockscreen. Whether or not I buy the for-cost apps on it remains to be seen just due to the compatibility factors previously mentioned.
It's quite a timely move by Cydia as well as there was a bit of a stink regarding the Apple App Store taking forever approving the Starplayr app for satellite radio. So long in fact, that the company that made it packed it in and called it a day. Quite a shame since I was looking forward to it. But I guess there's always room for another fart app.
Now, with the jailbroken app stores, those applications may get a second chance at life.