On the Community of Practice YahooGroup, John Smith raised the idea of looking at the community of software users in considering a big software purchase. Ending with this excellent piece of advice: "If you're in the market for software, look for the community around it."
Software companies don't tend to let you into their controlled "user groups" until you have actually bought the software. By that point it is too late to find out if it is the kind of community in which you can reasonably work. Software with large enough user bases, can obviously form user groups outside the walls of the vendor, and there is plenty of wonderful information available that way.