Haven't noticed any unusual battery drainage with Logmein Ignition...I've found almost all iPad apps to be pretty good about battery life so far, even games, after a version or two (the original Angry Birds seemed to kill my iPad battery, but subsequent versions weren't an issue)
I really love the Screens demos as well-for some reason I had thought it was only for controlling Macs. If we weren't so invested in Logmein at work, I may have tried Screens instead. Actually, I still might
Dropbox is just a perfect adjunct to any VNC app-love it.