Hi Vesa,
I've found out a little late that the 7.2 series is supposedly some sort of a "technology preview" branch. While I think it's totally irresponsible and moronic for the GHC devs to release a point release that's not supposed to be widely used [...].
actually, GHC 7.2.x is quite stable and it's perfectly alright to use it in production. It's been dubbed a "technology preview" because the compiler breaks backwards compatibility in ways that require library authors to update their code. Those who don't want to deal with that situation ought to stick to 7.0.4. However, those incompatibilities are not going to disappear by themselves. The 7.4.x release is not going to be different in that regard.
We'll have to think about if we really want 7.2 or do we wait for 7.4.
It comes down to the question: are you willing to patch lots of packages to fix compilation? If you don't want to do that, then you'll be stuck with 7.0.4 for quite some time. If you don't mind patching packages to fix compilation, then updating to 7.2.2 right now is a fine choice. Take care, Peter