I had a crack last week as I picked up a heroic bow and the rest of my gear is normal SoO or heroic ToT (ilvl 561)
I haven't played MM since WotLK during Ulduar with ArP (skipped Cataclysm) so I am pretty poor with it which probably has a bigger impact on most of the below then anything else. I really just stuck to single target with it, for example on Normal Garosh, I didn't even both with multi for the adds etc. I picked up Haromms during this week, replaced Heroic Rentakis, no other gear changes.
My thoughts, all 10 man:
H Norushen - fight length was almost identical, did 27K less dps as MM, and got in 2 stampedes. On our kill last week I stuffed up and only got 1 stampede out and it wasn't under RF or BL (whoops) so BM would have done even more. My target switching as MM to kill adds was terrible though.
H Sha - We are progressing on this. I did try out MM for the first few pulls, ingored the relfection adds, but did switch to the big add and the one left behind when someone goes pac man, numbers weren't great but not completely terrible, went back to SV where I am a lot more comfortable and did DOT up relfections with a Multi each time, but was doing more dps.
N Sha - Did 50K more as MM then my best BM or SV, ignored relfections, just attacked boss and the big add when it spawned. I did get really luck with gift of the titans though and our kill was 50 seconds quicker then my best SV.
N Malkorok - Did 70K more dps then my best BM or SV, but our fight length was about 40 seconds quicker, I think I also double potted this and I don't think I have done that since our first kill.
My thoughts really mirror what I have been seeing a lot of on the forums. Look I could definitely get better at it (well I could get better at SV and BM too hee hee) on single target (or where you role is single target) it definitely seems comparable. I actually feel if I got better I would beat SV single target right now because of the way my gear is, but there are just so many things to cleave / AOE onto I felt like I was missing out. I will probably keep playing it until I get 4 piece then go back to BM / SV. Depending on where my gear is at, I might use it to progress on H Iron Jugg, otherwise I doubt I will be using it for any other H progression bosses.
Log if you are interested:
http://www.worldoflogs.com/reports/8lxj572tb8njdy8o/
http://www.worldoflogs.com/reports/wyx0fjqxn1wh35nl/
http://www.worldoflogs.com/reports/9qkl0kud31w6ung6/