I've been beta testing MaxiVista 3.0.22 (beta) on Vista RC1.
Previous betas had driven me insane on earlier builds - and it was only in the past two weeks that I've started using it again.

I love it.  If you have more than one computer at your desk (or can have more than one!) this program makes it worth your time.  I have a desktop machine with dual 15" NEC MultiSyncs (two old 1545Vs) and my T40 connected together, and using this application, I can work on all three screens simultaneously.

It also offers clipboard synchronization (with file transfer support) as well as remote control capabilities on the secondary/tertiary screens.  The viewer software runs as a system service now.

I'd recommend it for anyone who wants more than two monitors attached to their system.  And yes, there's scientific research to support the increase in productivity too, to help justify the cost.

www.maxivista.com