I posted recently about Batch Apex, which I used to solve an interesting problem for data summary across lots of records. That code was working great before Winter 10 was released – unfortunately, Batch Apex is no longer working properly since the update. See this discussion for information on the problems people are encountering. The basic issue is that if your query is complex or returns a large number of records (the whole point of batch apex), it fails. I some cases you get an error, in others the query simply returns no records and reports that it was successful at running 0 batches.

If you were thinking of using Batch Apex in your own code, you will want to wait until they have a chance to iron out the bugs. I have submitted a case to support, and will post here when I learn more.

UPDATE 10/30: A release came out this week that appears to have fixed the issue of large queries. I haven’t had a chance to test all our use cases, but it looks promising.