Well, I just purchased the ATT Pure (Diamond 2) recently because the touch panel is dead after more than a year of usage (not consider HD2 or TP2 because of the Widcomm BT stack and I am a heavy A2DP user).
Then I missed my X1 so badly because:
1. X1 has a lot more hardware buttons (left, right, OK, panel, 5 way direction optical keypad & camera) for instant launch of apps (combine w/ AE button plus)
2. Less memory footprint. WM6.5 + Manila 2.5, and TTS on iGo8 works on X1 and somehow doesn't work on D2 (I am a cook and I already tune as much as possible on D2)
3. 3.5mm audio, handy for music and TMC antenna.
4. Flashlight as a torch.
Luckily, I fixed my X1 with replacement LCD+Digitizer and I am back to my X1 now. As other said, X1 is a very good device still if you know how to use it. The only problem is the case is indeed bad and very easy to crack (Just order the full OEM housing in ebay for US$70 in ebay yesterday)
My SE X1 rom-> http://forum.xda-developers.com/forumdisplay.php?f=471