Well, I can't claim to have had extensive experience with SourceSafe, but when we were doing our search for a new system to replace SGI's home grown one, we tried it out on a sample source tree, and there were a few black marks against SourceSafe:

1) It's slow. Perforce is waaay faster.

2) It's a black box. There are a number of converters to SourceSafe, but (at the time anyhow), they didn't have a way to get things back out. Also, if there's a problem with a file in perforce, it's just an RCS file. If all else fails, you can go in and edit it yourself and rebuild the file. No way you could do that with SS. There were a number of scary testimonials on the net about the SS database losing files, etc, but those problems were supposedly fixed in the 5.0 release (which I believe, but the scary part is -- what took them five major releases to *find* a problem like that!).

3) It doesn't work well for remote users -- there's no nice off-line work mode. Perforce at least thought of this scenario and provided tools for it. With our large number of remote workers (probably 15% of our engineers were several time zones away), this was a key point.

<flame> 4) It's from Microsoft, and it's not revision 7.0 or higher. This means it will have bugs, design flaws, missing key features, and a plethora of other unused and sloppily designed features. This may not be a bad thing from where you're standing, but for us, it was a key difference. Perforce isn't perfect, but at least they don't make the public design and test their software for them. </flame>

Also, I don't think you can run the SS server on a large UNIX box, and that was the only server we would have trusted to handle running our entire organization. Except for the reliability question, that probably doesn't matter to you, since a startup doesn't usually have 100 engineers banging away at the server.

(Man, I'm sounding like a UNIX bigot. Actually I develop only Windows applications these days. I just know that there are better things out there.)

Some good things about SS: it's Microsoft, so it's a transferrable skill, and there's probably a large user base out there. It's also probably more integrated into their product line than Perforce is.

Hope that helps.

-Greg.