My belief is that often Gmail is to some extent a testing ground for Google’s Business and Enterprise products and that in the next 6-12 months, we will see Google ramping up the featureset and integration of Google Apps for your Domain and pushing it as a product to customers. This will be done through Adsense referrals and possibly a more indepth affiliate program like that of Analytics. It is hard to say how many companies are using Google Apps, but it wouldn’t surprise me if there are quite a few. I know that PodTech does (link) there are a number of Universities who also use it.

It has been well documented that people are unsure about having their data hosted remotely, especially with the recent experience of data-loss at Google. It seems certain, that as the full integration of Google Talk, Gmail and Docs & Spreadsheets is complete, there will be a rack-mountable server that enables it on a local lan and integrates with their existing search appliances.