I've evaluated the field and definitely like NCrunch the best. Here's my feedback:

MightyMoose: The graph display is flashy rather than helpful, simple tooltips work better. The risk indicators are presumptuous and often innapprioriate. Having red and yellow lights that aren't warranted is just annoying. I don't really care about static v. heuristic prioritization as long as whatever the approach is performs well. And for me it does. Some tests were erroneously shown as failing. Doesn't continously test - you need to save first. Configuration is pretty basic.

.NET Demon: Continuous save is a horribly broken feature - exploratory changes to code without wanting to save is something I do many times a day. Tool tips are good but not as detailed as NCrunch. Very basic configuration.

Giles: Needs to integrate with Visual Studio because that's where all my workflow is. Sorry!

NCrunch: A clear winner - continous test reacting to code changes without saving is perfect. Level of feedback onscreen showing code coverage and execution times is the nicest of all the tools. Love the exception details. I do think it would benefit from it's own tray-lane as it does interfere with R# bulbs and this is a minor annoyance. We have a lot of multithreaded unit tests that use WaitAll() which NCrunch can't handle in 1.38b due to use of STA thread - this is a major annoyance but I am sure it will be fixed. The level of configuration is great. Works well with source control for persisting solution settings and omitting user-specific settings. Decent manual/wiki on the website which others lack. Not sure how useful the risk progress bar is... I don't really use it. The corner indicator is great! Shows really useful info with just the right amount of presence.

Feature suggestion: Extend code coverage to work like dotCover with actual code highlighted, use tray-lane for performance data/test coverage.
Business suggestion: Do a deal with Jetbrains! This product has great synergy with R#/dotCover, and I'm sure they'll have something competing if you guys don't colloborate. I would be totally happy to pay for this product.