However, since installing it, if I leave my PC alone for about 10 minutes, it takes me back to the log-in screen - the screen were you choose a user account. Anyone else getting this? I'm not sure I like it doing that.
Check your screensaver options?
I'm running Catalyst 5.3 myself (Radeon 9600 Pro). I tried the 6.x version, but absolutely hated the color profile adjustments that I needed to make my display look good --- 5.3 gave me more control over those than version 6.