Synchronize data with SalesForce.com to Search!
Now you can create an index via customized fetcher, and select the SalesForce.com adapter, fill in username/password and the object you want to search on, like "Account".
The rest is exactly the same as ordinary database search configuration.
The good thing is, the incremental indexing will also work. You just schedule the job. And on SalesForce.com side, you need to make the object replicable. This replicable setting doesn't matter if you create index from scratch.