Update: So, scratch all that. Steve Kondik took to G+ today to say that CM will return the opt-out option and will not require users to share data. Though it's with a heavy heart, it seems. Expressing some exasperation, he had this to say on the matter:
It's incredibly frustrating that a handful of incredibly vocal users are ready to "fork" over the issue. News flash: there are already a hundred forks of CM... In the end though, we should respect everyone's wishes here.
CyanogenMod is one of the most popular Android ROMs as far as anyone can tell. It's actually hard to know for sure.