Version Control was not a big thing as long as I was doing freelance development. But once I got into the process of working with a team I released that a Team programming without source control is useless.
I started using CVS with the WinCVS client .. Then moved on to use Sub Version with the TortoiseSVN client..
I spent most of the last 2 years in Microsoft world .. So Team Foundation Server was the system..
Right now IM on Ruby and we are using Perforce which is actually Damn Good !
Ther user interface is damn simple although it might look a bit funny.
Its one the systems used by development teams which work on various platforms ..
I can check in code from my windows box and get latest on my Linux box / server ..
This is really cool !!