Our former Source Control was VSS. We primiraly changed becuase of its unreliablility and very poor WAN support.
Why we love it....
...the most important thing in my opinion are those atomic transactions implemented by vault. This is a "must go away from VSS" if you're seriously developing software and if its code is the capital of your company.
...The second and deciding reason was the offline capability. We can say that there's no difference in performance and responsivness whether we're working via LAN or WAN (2MBits)!!!
...Another really cool feature is the extensibility of Vault by programming against its Web Service interface. If this is to complex you can simply use a command line client to integrate source control in build automation etc.
...SourceGear's support is outstanding in short response time and high quality.
Some things you should know...
...even if Vault is implemented based on state of the art technology its not necessaryly faster as Visual Source Safe. In our LAN the time required to retrieve our complete source is almost the same comparing Vault to VSS.
...there still are some minor restrictions. E.g. you cannot checkout a file to a destination other than its working location. You cannot drag&drop files, move files.
...the SDK and command line client are poorly documented and unsupported which would be a must because we need to maintain our build machines.
...the IDE integration of Vault is very, very slow in some situation (which is caused by the way VS.NET controls Vault but that doesn't change the fact...).
Overall we're very happy changing to Vault! I hope you guys at SourceGear will be bought by Microsoft and Vault becomes the industry standard source control
.Regards, Alex