I am currently running the Softube Tube Delay on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run the plug-in in Pro Tools LE 7.4 that run with either a Digi 002R audio interface or a Digidesign Micro Box. I've never had any troubles running this plug-in with this configuration, although I only tend to use one or two at a time on an auxiliary channel in order to save processing power (I do this for all delays and reverbs). As long as you use aux channels you shouldn't have any problems running this plug-in and even if you wanted to run a bunch of them at once as long as you have a good system you should be able to do it.
I've only been using the Softube Tube Delay for a few months, but it has become one of my favorite new delay plug-ins. It has a really warm sound for a plug-in and is capable of getting a variety of different delay sounds. Have the option to add drive to both a wet and dry signal is really cool as you can do some nice blending. I also like the tempo synch switch as it does a good job of synching it up. The price isn't all that cheap, but is reasonable for the quality that you are getting here. All in all this is really nice delay plug-in, but definitely check out plug-ins like the Line 6 Amp Farm and the Moogerfooger Analog Delay as well as a slew of other delay plug-ins on the market, as there are a lot of great ones out there.