I just got M-Audio Torq/ Connectiv with control vinyl yesterday. I'll be using it mainly from a DJ/ Turntablist point of view.
I've had a quick play on Serato before and the M-Audio set-up seems pretty similar.
Very slight latency I think (nothing that can't be compensated for). Also seems to have occasional problems with the current track skipping/ lagging when you try and load the next one simultaneously - but I think this is due to having only 256MB RAM. System requirement is 512MB and I'm getting an extra 1GB today so that should hopefully sort it.
Scratching and doubling/ juggling is totally possible and overall the package promises to be great fun, good value also at £160 (UK price from online mail order).
I will have some tracks/ skits recorded using it soon which I'll post at
http://www.myspace.com/analogueonthecut.