I use this on my Macbook Pro (2.2 Ghz, 2 GB Ram) and I've had no issues at all with it. I use it on an auxiliary track with every session I do. This saves processing power; if I were to put this plug-in on every track however, I do believe it would slow down my computer quite a bit. This is to be expected with any sort of powerful plug-in such as this one though. As long as I keep it on one track or a few at most it runs great.
I've had it for about a year now and it is the only reverb plug-in that I use - its that good. Not only is it really easy to get a nice sound from it, but the controls are really in depth and useful. I've used a a couple of reverb plug-ins in the past and this one trumps them all. While I haven't done this, I believe that you can download extra presets for it, a great feature that I will look into when I have a chance. Even though it is definitely a bit pricey, for me it is worth every penny. I've used an EMT 140 plate reverb and the emulation of that on this plug-in is impeccable. If you are looking for a serious reverb plug-in, spend the money and get this; you won't regret it and you will have a great sounding reverb for all of your sessions.