I've been using an ST2220T for about two months now, and its a mixed bag.
On the one hand, its a great monitor. Think 1080p version of the 20WMGX2. Its really that good. I have a preference for "glossy" displays so I especially like it. I'd say it might even almost be worth the price just as a display. From what I've seen its also good about input lag and ghosting (again, reminds me of the NEC).
However, the touchscreen is...well its not up to touchscreens in phones/tablets, let alone a real alternative to a digitizer. Its ok for simple touch, but its not precise or fast enough to do much serious digitizer style stuff. Its cool that you can use basically whatever as a stylus (which means you can get something that won't scratch up the screen, I've been using paint brushes for instance). I did some sketching in SumoPaint and its ok, but can be an annoyance (as there's an onscreen mouse that wants to pop up and can cause you to hit it when you're just trying to draw, and unlike with a cursor you can't disable that without disabling touch altogether). You can do some ok sketches, but if you're serious about doing anything like that, even an off brand (non Wacom) tablet would be a step up. Its not completely unusable, and it would probably be fine for testing apps for touch devices.
I've had mine listed in the FS/T forum as I planned on selling it and going dual monitors, however I haven't really been able to find a serious alternative to it just as a display. Ideally I'd get two 20WMGX2 (I already have one that I gave to my Mom, so I could get her a different display), if I could source one, but I can't. I'd consider going with a single 27" Apple but its just too much (and I'd have to also get a new video card for Displayport), so I'm kinda stuck at the moment.