I actually have tried this when it was at version 8, wasn't impressive enough I have to say. The fatal part was that it doesn't show gmail and some banking sites correctly hence I dropped the idea of further testing it.
This version at 8.5 is a lot better especially the free version doesn't have ads, that's a big plus. Have just tested out the "lightweightness" of it. It requires from 31 - 38Mb (5 tabs) while Flock is marginally less at 24-35Mb (5 tabs). Firefox is heavier at 47-55Mb (5 tabs).
I think Opera is better than the AOL explorer or the latest Netscape based on my 1 day long trial.