I have an XT LIVE connected to my PC that I use as a part of my practice system and run it thru headphones. It's incredible as a teaching/practice tool especially when tied into the Line 6 Website.
I also use it strictly for effects on my live rig. I don't use the amp simulator and the effects are very nice and allow me a tremendous amount of flexibility. A real benefit is that I can dime my amp out and then adjust the input volume level to the amp using the line level adjustment on the POD. If something ever happened to my amp onstage, i could plug directly into the PA system and keep going.