I made a pretty big mistake the other day. I installed Visual Studio 2008 Team Suite on my primary desktop workstation. Instead of doing the smart thing and installing it side by side with Visual Studio 2005, I uninstalled Visual Studio 2005, then installed 2008.
The main reason that this is a bad idea can be summed up in the following picture:
Because I uninstalled VS2005, I broke SQL Server Business Intelligence studio. Since most of the code I interact with on a regular basis is SQL Server related, this is a problem.
In order to solve the problem, I have to reinstall SQL Server 2005 Workstation components and then reapply SP2 for SQL Server (and the subsequent rollup patch). All in all a pain in the neck.
Don't make this same mistake!