I'm going to have to disagree with the idea of forced upgrades.

If you want to implement some nagging system, that's fine. There's already the "there's a new version of Limewire" message, that has previously included information about why it's absolutely necessary to upgrade. But, in the end, it was still my decision to install the new version.

I don't see the reason for taking the step from strong encouragement to force. It's enough to make some people suspicious of what all is included in the upgrade and possibly switch clients (or, edit the source to bypass the check).