The T-Mobile myTouch 3G Slide is known as the HTC Espresso. I've been running CM6 on mine for weeks now using the nightly builds produced by their build-bot. There are a few outstanding issues on the device that may give you pause, however:
1. Bluetooth audio is nonfunctional for phone calls
2. Wifi connectivity issues arise in certain circumstances
3. The "FN" and "CAPS" lights on the hardware keyboard do not light up when their respective buttons are pressed
Other than that, though, the software is rock solid. I'm even running an overclocked kernel on my Slide, bumping the max processor speed from 600 MHz to 844 MHz without any loss of stability.