I donated to the TX developer to get in on the beta, because it looks so smooth and good on other phones. It runs like crap on my Omnia II SCH-i920. Jittery, stuttering, shuts down for no reason.
What it comes down to is Samsung writes awful drivers. Their OpenGLES2.0 drivers are terrible, they didn't even bother to write drivers for either the FPU unit (it's just sitting there doing nothing) or OpenGLES1.0. They override a lot of Windows Mobile's APIs with their own proprietary junk, tied to TouchWIZ which is a joke in itself.
The bottom line is, it took a lot of customization and extra cash for a third party UI, just to make my phone as useful as last year's models.