software

They have been getting great reviews and it should be way better than the Line 6 Guitar Port.
Sounds like they could be a great addition to a home studio and for practicing.
I like the idea to be able to bring great sounds for direct recording with me, as I would use it with a lap top.

Anyone ever used one of these?

I used it. It's really good for laying down quick demos and for effects on vocals and keyboards. It's also great for taking a recorded track of guitar and adding various types of ambiance and effects (stereo positioning, reverbs, tremolos, etc). I don't think the amp models sound very good though. I wouldn't use them for anything serious.

I have it. The clean models are decent IMO, but for overdrive I prefer Amplitube. For effects I prefer Waves. Guitar Rig has lots of nice features, it's really an all-in-one type solution, though.