this has to be my favorite setup, I have been thinking about downsizing to a setup type like this, but not so sure if I want to move my iMac away.
thats very similar to the setup i had.
i went from a 20" alu iMac to a 13" uMPB set up similar to that and i havent looked back since. my imac kinda just sits in the closet collecting dust right now.
The one thing i do wish i had though was an external monitor for watching the masses of movies and tv shows i have.
sell the imac, buy an external monitor, upgrade the ram and hdd of you mbp. this way you have a very capable desktop and monitor when your at home and have that same power in a portable solution when you need it.