Many times development managers face tough choices when they need to decide which source control repository to use. Some would like to go for commercial vaults like SourceGear, SCM etc. Others prefer open source tools such as CVS, SVN, SourceJammer etc.
In my opinion the open source repositories are pretty decent. I have seen many big organizations use CVS for large commerical projects successfully. What I like best about CVS/SVN is that they let concurrent development, whereas SCM, SourceJammer and VSS(if multiple checkouts are disabled, which is done generally). does not allow such luxury.
Only care that needs to be exercised is that developers should know how to merge/update successfully. People generally misuse such features like I have seen many people using Force CheckIns everytime in SourceJammer.
Also, many of these open source repositories have extra tools for GUI and Visual Studio/Eclispe integration, which makes them all the more attractive.