I'm currently running QuikQuak's UpStereo v2 on my system at home, where I've got both Pro Tools 9 and Logic Pro 9. I've used this mostly in Pro Tools, but as I said earlier, since it's not an RTAS plug-in you'll need a VST to RTAS converter like the one made by FXpansion. I've used the plug-in only a handful of times, but I've yet to have any issues at all when it comes to performance. Most will be using it on the master buss anyway, so performance shouldn't be much of an issue in general.
Being that it's a free one, it's kind of silly not to add QuikQuak's UpStereo v2 plug-in to your DAW as long as you've got a compatible system. While there are indeed a bunch of free ones out there that serve this same purpose, this will stand it's ground with any of them, as it's one of the best stereo enhancers I've used to date. While this type of plug-in isn't something that I'm going to use very often, when I do I'm definitely going to use UpStereo in the future.