I'm using 37signals' Basecamp webapp for collaborating with many people on data standards. Generally I like the product. There are a few issues like not being able to easily follow a topic or wiki ...
In Writeboard, if you enter -- (two normal dashes/hyphens), it gets displayed as — (one em-dash). That's probably fine and cool in most cases, but gets annoying if you'd want to document e.g. Unix ...