Hi - I installed Lion this weekend - I have a PCut and use SignCut Pro.
Didn't work right off -when upgrading to Lion it looks like I lost the drivers to the keyspan.
The fix is that you need to reinstall the latest driver for the keyspan on the system. www.tripplite.com - do not use the CD that came with the keyspan - it doesn't work (also note - the latest driver says 10.6 I think and Lion is 10.7 - but it still seems to work)
After it is installed re-start your system and open SignCut (that's what I'm using).
Select cutter
In the Output Device section select the keyspan device (for me this was /dev/cu.usa19Hfd13p1.1
Now I'm back up and cutting!
Good luck