Had the same discussion with a friend a while back.
Had to choose between a "high" cap, unshaped connection or a shaped uncapped, decided that the pain and effort involving uncertainty and the pain of monitoring just isn't worth the increase in speed.
It's just so much better to know I always have a connection (at a set price). You never know when you have to reinstall a machine and download tons of service packs and updates (took me 1.5 days of downloading in a 4Mb line for Win7, Visual Studio, Office, SQL Server etc. updates)
Not to mention having to sync your entire email account to a desktop client if your backup doesn't work for some reason...
Uncapped FTW!