I’ve been using an early build of ReSharper 4.5 for a couple of days, and must say I like it quite a lot. I tried the latest tested nightly build, and the first thing I noticed was the improved performance. I don’t have any empirical data to support my findings but Visual Studio seems to be a lot snappier than with previous versions. Devenv+ReSharper still likes a lot of memory, and I haven’t seen any significant change in that respect.
Another cool feature for us that use Microsoft’s unit testing framework is that ReSharper now supports this framework in addition to Nunit and a couple of other testing frameworks. You can run your tests in ReSharper’s test runner, and you can also profile your tests if you have dotTrace Profiler installed. The current build only traces ReSharper’s own test runner code and not any of my code, but I expect this to be fixed in later builds.
If you use Team System, I think Visual Studio’s test runner is better in most cases because it’s better integrated. You can for instance submit bugs to Team System based on the result of the tests, but if you only have Visual Studio Professional, ReSharper improves how you manage and run tests.
Please note that this is still an early build, but If you want to try it yourself you can download the nightly builds from JetBrains ReSharper Early Access Program: http://www.jetbrains.net/confluence/display/ReSharper/ReSharper+4.5+Nightly+Builds