I've been in IT for quite some time now and work for a large nonprofit in the upper midwest that recently moved to common ground/salesforce from a traditional client server solution. In addition to Common Ground I also have access to and work with Raiser's Edge.
The fact of the matter is that people, not software per se, generally determines the effectiveness of whatever solution is applied to the challenge of tracking people, transactions, and the many types of relationships nonprofits need to mange.
Consequently, instead of tossing the proverbial note in a bottle on slashdot and seeing what comes back you should be polling your users, your IT staff, and those that do or can understand what your organization is both capable and incapable of using, supporting, and growing.
Next, organize it, prioritize it, and cost it.
You will find that what you need from a nonprofit-centric crm is unexpected, hard to document, and not easily matched with any one tool on the market. But at least by taking the above approach it is your requirements, and not vendor brochures or the emotive proclamations in this thread (present company included), that will drive your selection process.
For my organization with IN PARTICULAR the common ground/salesforce platform works well. You have different needs, most certainly, and what works for us may not work for you.