Definitely an improvement
To have these things baked right into the OS without having to download 3rd party software is pretty nice but there some features of that software that are still attractive but because they haven't been updated for use with Win8, some things are a bit buggy when you use that software. For example, using the ATI software for Eyefinity doesn't set/reset properties correctly when you switch between Eyefinity and traditional displays. Of course it's all beta still so you can't really complain.
Having multiple monitors with Metro is definitely better. I, like you, stick metro on the left monitor and use the desktop on middle and the right. I had traditionally used the left monitor for Outlook and Instant Messaging but now I'm filling it with Metro Mail and snapping Metro Music/Messaging to the left side. One thing I'd like to see Microsoft do is allow Metro to go multi-monitor even if they keep the snap, fill options. For example, snap Music to the left edge of the left monitor, fill the left monitor with Mail and then let me snap Messaging to the right edge of the right monitor. That way, it preserves the snap/fill style of metro but makes it more multiple monitor friendly.
