I've been working on a project lately where there are elements of Web 2.0 (specifically Ajax stuff) that keep being raised, almost without thought for form or function.
The end result is that I've forced the client in question to seriously consider why they want to do something, and what the benefit to the end user is. Of course, this adds caution to future thinking!
One of the things that I keep banging on about with clients, is the importance of the user, and how they experience the client's brand and end up leaving the site. At the end of the day we want the user to leave happy and contented, but we're not going to achieve that if we're putting obstacles up that make it difficult.
Ajax is one of those things that can easily be overused if not done in the right way, or simply done everywhere - so I've started asking questions like "how does the user benefit from that?" before asking the client why they want to do that. Instead of making the client defensive about their ideas, I'm asking them to consider the broader implications of what they're asking for.
Similarly, you can extrapolate that across any project you're running where there are elements of new technology, or for want of a better moniker, Web 2.0.
So far, with the clients that have cottoned onto this Web 2.0 thing - the key has been to restrain them from wanting to do something simply because it's new and shiny, but to continually focus on how whatever we do will affect the user experience, of which the corollary is how that will affect their bottom line and also the project cost.
Usually, this results in the Web 2.0 stuff ending up at the bottom of the "nice to have" list, with the focus re-emphasised on doing the basics consistently - followup, measurement, content, feedback, search. There's more than enough to be busy with there!
This is more of a ramble borne out of frustration than anything else - but I also wanted to get across the idea that silver bullets are very hard to find, and you're normally not going to find one when the werewolf is bounding down the corridor!