Run tests when save or build would be great.
Run tests on type is not a big problem for my desktop PC, I put NCrunsh's workspace data on a 4GB RAMDisk.
But next month I plan to get a Microsoft Surface Pro. Run tests on type would be a problem because Surface Pro has only 4 GB ram, not space for RAMDisk, I have to put NCrunch's workspace data on SSD. I'm quite worrying about lifetime of SSD (NCrunch writes 1.2GB of data on disk each time I open my main solution (37 projects, lots of references)).