What's amazing here isn't that there are rich clients on the web that use an asynchronous tier. What's amazing is that they aren't built using proprietary technology; they're not Flash, Java, or ActiveX.
Because they're not proprietary, we can, as JJG says, use the techniques we already know and are well deployed. This is also true for scaling Ajax applications; we can use the stuff we already know; Etags, Range, If-None-Match, etc.
# — 21 February, 2005