I can't say that I've ever had a problem running this plug-in. I'm currently running it on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run Pro Tools LE 8 with a Digi 002R audio interface or a Digidesign Micro Box depending on where I'm working from. While I haven't used this plug-in very much beyond initially trying it out, it isn't the type of plug that will take up too much processing power. If you're currently running some plug-ins in Pro Tools on your system without a problem, you'll definitely be able to run this one without a problem as well.
In general I'm not a fan of distortion plug-ins, so maybe I had a bias going into using the Digidesign AIR Distortion, but I just don't like the sound that it produces. I tried it on vocals, clean guitars, and bass guitar, and with all three I got a similar type of digitally scared sound. While there is a good amount of versatility and I do think that some people will find this useful, it just isn't for me. I always try getting my overdrive sounds from the source rather than a plug-in anyway. If you have Pro Tools 8 I'd definitely encourage you to try it and judge for yourself...