Ya the real-time rendered scenes go back to 16:9 (maybe 16:9, i dunno), but the screen edges slide in, so it's not a clunky transition. for getting the HUD back from behind teh bezel, there's a setting in 'Display' section that let's you bring it towards the centre a bit, which was nice to see. I only played for a few minutes, but I didn;t see any glaring issues with multi-monitor. Kinda expected, since the GTA IV support was pretty good.
I'm super-impressed with the crazy amount of graphics options and how freaking well it runs. I maxed out most options the the lowest i saw my fps get was 41fps. On a 4.4ghz 2700k, 2x 7970's, and 8gb ddr3.
Of course, Both nvidia and AMD have newer drivers for this game. The AMD Betas already have tweaks and a Crossfire profile. While I'm on the topic, enabling Crossfire took that hardest benchmark scene from 24fps to 41fps. Nice.
http://support.amd.com/en-us/kb-articles/Pages/latest-catalyst-windows-beta.aspxI've yet to much around with it too much, but there's a lovely little settings.xml located in \My Documents\Rockstar Games\GTA V\
I've also found that if i disable the DOF option, my game crashes when i go to the pause menu. Lame.