PbF roleplaying can be fun, but I think it's harder than FtF roleplaying. It's much easier in FtF roleplaying to communicate a lot of "character" through non-verbal signals, and to have quick back and forth (i.e. "I try to do X", "okay, roll these checks" <rolling> "here's what happens".) PbF roleplaying is also more prone to stalling out than other games because it requires an investment not just in "playing" but in participating creatively. The previous thread on this topic, brought up PbF without a system, which can work better (because it's less game and more straight creative-writing from everyone), but personally I don't like system-less roleplaying.
With those caveats, I don't get much chance for FtF roleplaying these days, and would be interested in some PbF. I'd be happy to run something like Deadlands or Mage: the Ascension, but would rather not do DnD.
Something like InvisibleCastle can work well for having everyone roll their own dice and having it be check-able, rather than needing the GM to do it all.