I have the same problem - but I don't have Hide User Agent.

I can browse the Ovi store, but "Preparing for installation, please wait" stops around half way.

I can di & install fine from maemo.org & extras & devel - just not ovi.

The most annoying part is I uninstalled Angry Birds & Bounce to be able to upgrade to 1.2 OTA, now these are the only things I can't re-install.