a) 'google' your hard drive application. Now, the G hasn't been too good when it comes to cross-platform apps (the IE toolbar), but using Java may allow them some freedom from the vicissitudes of Microsoft -- and you know M$ is gunning for them.

b) tools for developers. M$'s great success is at least partially built on giving developers what they want: great tools. As you suggested with Eclipse, perhaps the idea is too build easy-to-use tools. For instance to build custom apps which hook into google web services.

c) file sharing. 'google your peers'. They could increase their power by making an app that becomes THE way to transfer files and share/search data.

d) extend the google appliance. This is really speculative, but what about extending the search engine to run second-order stuff on a distributed farm of perhaps millions of volunteer PC's? For instance, crunching through indeces to improve the results of a particular topic, weed out page rank abusers, etc.