The concept is interesting but not new. In fact Windows Vista does something similar when downloading executable (putting them in a sandbox to see that they try to do) applications from t'internet.
Also most decent AV programs have heuristics which should pick up malicious software code by the actions it takes, and a firewall should stop any keyloggers reporting back.
Really it is about making security simple for people to incorporate into their lives - personally I use a program called locknote (freeware from steganos) to store all my passwords. It's basically a tiny encrypted (256bit AES - near as damn uncrackable) notepad application. If i'm being really paranoid I launch a virtual machine and run the applications within that. More secure would be to run a linux distro. I'll definately be keeping an eye on Finjan's work though, it'd be interesting to see a plugin for opera as well.
Havelock