First off I'd like to say that the new online Market is pretty great. I really like hitting the "Install" button and it goes straight to your phone. If you use a site like Androlib you use the QR code to take you to the Market on your phone.
That being said, I found an interesting difference between installing an paid app. I'm talking about the apps that you paid for, but have uninstalled them after the refund time is long past (maybe you need room or didn't like an older version). In theory you don't have to pay again if you want to reinstall it.
Well, that depends on where you're getting the app from.
If you go to the Market on your phone, the app will say "Purchased" and all you need to do it press the button to reinstall it. If you go to the Market online, it wants you to pay for it again.
Just keep that in mind if you're looking at the forum and saw that maybe you were too hasty on removing that paid app and want it again.