I recently downloaded and installed the Sonalksis FreeG plug-in, grabbing the RTAS version for Mac as to make it compatible with Pro Tools. I'm running it on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM, while I run Pro Tools LE 8 with a Digidesign Digi 002R audio interface. I've been able to get one of these up on every track in a session without a problem. That said, it was a sixteen track session with no effects yet. Of course if you use this as a master fader it will take up even less processing power...
For those who don't have the Sonalksis FreeG fader, do yourself a favor and get it right now! It's really a great little plug-in to have around for a number of reasons, and even if you don't end up using it there's really no harm in having it around just in case. It isn't going to affect your sound at all beyond what you set on it, so it can really only help you. If you are used to large console, it might definitely be helpful to have this in there as it gives your DAW an overall more realistic feel. The FreeG is definitely worth more than what they're asking!!