Bandwidth. Just one more thing, Matt. Sounds like you're just getting familiar with RSS. If you're not familiar with how to set it up, I'd suggest you do a search for how to handle the bandwidth regarding RSS. If you don't set things up right on the server side, you may find yourself nailed with a huge bandwidth bill.
The centralized aggregators like yahoo and bloglines only poll your feeds once an hour. But when someone downloads a client, they might set it to check every minute. There are solutions to limit its impact. But if you don't do it, you could have a huge bandwidth bill.