So now let's talk about some of the things I don't like about Vault, lest this seem more like an infomercial and less like a real review. Fortunately, there aren't too many of these, and most of them resolve around one thing... licensing.
Vault's licensing model is not the most flexible thing in the world. You'll find their latest pricing sheet here. The starter pack is only $599 for 5 licenses, which is quite reasonable and is what I have. However, after that it starts getting steep. For one more developer, you need to pay $399. In fact, for another 5 licenses (basically, double what you got for $599), you need to pay almost $2000 ($1995 in fact). This seems to work in reverse to most licensing models, which have relatively steep individual prices but discounts for volume. I assume that large enterprises can contact SourceGear to get discounts for their hundreds of developers, but small shops with a dozen or so developers are going to have to swallow these costs.
To be fair, the prices aren't that far from what individual licenses for VSS cost, but most developers use the VSS that came with VS.NET (which may have come with their copy of MSDN Universal), so they're not used to seeing that as a separate price to pay. What's more, with my VSS license, I can connect to anybody's VSS repository, because I have a licensed VSS client. The other issue I have with Vault is that there are no client licenses. Every server must have paid licenses for every user account. So if I have a server for AspAlliance and another server for a client I'm consulting for, I need to pay $399 for a user account on each server (well, somebody has to pay it). I don't like the fact that I have to pay multiple times for the use of the tool as a client, and I hope they will support client licensing in the future.
Other than that, I don't have a lot bad to say about Vault. It hasn't eaten any of my files. It works great with VS.NET. It does what it's supposed to do. It's slower than not using any source control, but faster than VSS. It's being worked on feverishly by the guys at SoureGear, who will answer your emails within 24 hours typically when you post to their Vault Mailing List (a great place to lurk to learn more about what's going on with the product). They've gone from a 1.0 product to 1.2.2 in the last 9 months or so, with lots of stability and performance improvements along the way. The upgrades haven't lost any files or data (from my experience), and the latest updates didn't even require upgrading the client.
All in all, I've been very satisfied with Vault, and unless Microsoft releases a very compelling source control solution in the very near future (which seems quite unlikely), I think I'm going to be using Vault for a while.