The theme I keep arriving at over and over when I come across new Web 2.0 technologies -- or any new technologies for that matter -- is this: What is the problem I'm trying to solve in the first place?This is a great warning of keeping the bigger picture in mind when working with a client to meet their goals. Whether you're working with a business, nonprofit or other entity they all have particular goals they want accomplished -- they all have particular pain points to address. Don't throw tech at a problem and expect them to be all excited.
Take wikis for example, they do a lot of great things. But are they right for all clients? Just look at the difference between Esquire and the LA Times with regards to wikis.
Looking back, the key takeways from the wiki examples still ring true for me. I also would add that in addition to knowing "the pain points" one must also have keep the bigger picture in mind: institutional buy-in, a plan, and ongoing refinement.