As many others, I've been struck by pirates. Ovi DRM just doesn't work. Some have suggested a commercial licensing software but I don't think this is necessary at all.
A cheap solution that would work for me is "purchase notification". Basically, when a user buys my app, I'd like to get an email with information that will identify this customer - ovi username, "transaction number", maybe also phone number and IMEI. Transation number should also be provided to the customer. It could also include some other convenient field that Ovi keeps, and some of the info could be hashed to protect end user privacy. In any case, the info has to be enough to uniquely identify user and their purchase.
This would give us something to work with. If this is provided, tools & APIs for using it will quickly spring up.
I understand that not everybody wants to bother so this can be opt-in. At some point, Ovi can develop a better solution, but this sounds like a very cheap trick that can solve a big and expensive problem.