Wow, it's been a while since I've posted here. Haven't takeen a look at Planescape at all until recently. Since the release of Warriors and Warlocks (the fantasy supplement for Mutants and Masterminds), I have been pondering the prospects of Planescape in Mutants and Masterminds. I did a search for previoius threads on the subject, and found that at least one person had run a Planescape game using M&M.
As I look over the past discussions, one of the main difficulties it seems was due to the bugaboo of simulating the D&D, Vancian magic. Would the Magical Mastery power from Warriors and Warlocks address this, at least partially. Basically, it's a Variable Power Structure that requires you to spend an hour preparing (via spellbooks, prayer, etc) to reallocate your power points into the various desired spell effects, subject to the restrictions of your descriptors.
On a more general level, I'd love to hear about others' experience with it and thoughts on it, as well as plots you've done or might think up that takes advantage of the system. I have been tinkering with some archetypes and templates myself.
I'm not familiar with the new release - but would love to see a full conversion writeup for the system. It's one of my favoriate superhero systems. Let me know if you do a full conversion, we'll gladly host it!