We are using Subversion and TortoiseSVN and find it invaluable for customer support when tracking down bugs. Several times we have needed to go backwards in time to pinpoint when a change was made, and this can drastically reduce the debugging time.

We also use it heavily for projects with multiple engineers and it works well. Including the times when we needed to find out who made a specific change (the 'why' is either in the comments or in email discussions).

Another major use for us is to keep track of code we send to clients - each copy automatically has a unique revision number.

For Flash Magic the Subversion revision number is appended to the program version, helping to improve our quality control along with bug tracking. Releasing two different versions of a piece of software with the same version number is a big mistake, but easily done by accident. So we handle this automatically using a script that ties into Subversion.

Andy