I also would like to add my voice to how much better Vault is compared to SourceSafe. On my last project, with 5 developers spread across the country, we attempted for a few days to use SourceSafe over VPN. I was in charge of installing and setting up this scenario. In a word, it was horrible! Performance was terrible.
I quickly went to SourceGear because I had used SourceOffSite (also by SourceGear) a few years back on top of SourceSafe for a similar remote development environment. I was pleasantly surprised to see a complete replacement of SourceSafe written in C# and using SQL Server (you can also use MSDE). I quickly voice my concern to the team that we take a look at the product. It was purchased, and everyone was all the better for it! Even when we had to move from a VPN setup to a straight Internet-connected setup at another location, Vault worked flawlessly! We switched to SSL, and once again, everything worked flawlessly!
For my own personal development, based on this experience, I am looking at purchasing Vault and recommending this product to others as well. Sold to another satisfied customer!