Having spent all morning trying to check something in - I now realise I've lost a couple of days worth of work.

Its happened before - and is apparently common occurrence with SourceSafe.  Can SourceSafe be used successfully, without problems, and if so, how?

My view is simple, migrate to something else ASAP. It won't take long (1-2 weeks WAG) and no matter how long the migration takes, it's easy to cost justify that to management. A little time to migrate equates to solid source control and very little chance of lost source code. Do a quick google search for "source safe horror stories" or similar if your boss is skeptic.