In my home studio I'm currently running Cytomic's The Glue buss compressor in Pro Tools LE 8. I run Pro Tools LE with a Digi 002R audio interface and on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. Generally I'll only used The Glue on an auxiliary channel for drum bussing or something of the sort, so I'm usually not putting it on individual tracks. Using it this way I've yet to have it slow down my system in the least...
Overall, Cytomic's The Glue is some of the best bang for your buck out there for a compression plug-in. It has a very full sound that is fully adjustable across the board, giving you an almost endless array of possibilities. I definitely like using this mostly for drum bussing, as it has the potential to bring your drum set to life without too much fiddling around. While not as good sounding as the SSL licensed Waves buss compressor plug-in, it still sounds awesome and is actually a bit more versatile. I'll definitely take the trade off in sound as The Glue cost a fraction of what the Waves SSL Collection will cost you, as it's only $100 US dollars. At this price it's a must have for anyone interested in a great buss compressor on the cheap.