- Don't try to replace standard GUI components with inferior and non-intuitive substitutes. The Wave scrollbar was a user interface disaster, and a source of frustration to many of the users I interacted with.
- Don't promote technologies that depend heavily on high-bandwidth connectivity, or at least not for Internet use. Many times I was left frustrated, not knowing whether the Wave had crashed or whether it was simply waiting for a server response.
- Realize that even the best technologies need marketing and publicity. 80%+ of desktop computer users don't use Windows because it's the best system, they use it because it's the best alternative they know about. If people don't know about your technology they won't use it, and techies alone probably aren't the right user base to make a product viral.
Google's misstep with Buzz earlier this year probably didn't help either - it led to distrust about Google's intentions with regard to (or, worse, competence at securing) users' personal data.
So whatever the next big thing on the Web is going to be, it isn't going to be Google Wave. RIP.