Why does my 3G phone keep getting slower?

Does anyone else have this problem? Its seems like as more time goes by the phone just gets slower and slower. It reminds of the days when I owned a PC. Email seems to be the worse. Especially when you are going from folder to folder or start composing an email... it will just freeze for awhile then just start working.

I've rebooted the phone each time and that just doesn't seem to fix it. Is this a case of too many apps? Or, just a combination of the wrong apps? Based on what I read I believe I'm about avg regarding the number of apps.

Any thoughts?