I have completed my first half of the double CMB MR and can say this is very easy to do as far as getting to and from all the airports. It may not be for the weak at heart because it is a lot of flying and time in an airport.
For anyone who is worried about getting to CMB and not getting out, don't! This has to be the easiest turn around I have ever done because you are on the same plane that brought you out there. No problems at all.
I can say I will do this again next year if these rates still are valid. This way I can say for sure I will have two MR to SIN each year with my little trip to CMB.
If you want to see how it went for me, find my trip report at
http://www.flyertalk.com/forum/showthread.php?t=489821 and I will update this once I'm completed with the second half here in a couple weeks.
Take care and enjoy your MR if you have it scheduled. It really is easy.
On a side note, if you do a MR, don't forget to add in the extras (hotels, taxi, food, etc.) into the trip. When you go out of the US, you have to look at the exchange rates and how that will also effect your total cost. I can say that SIN is not that expensive to go to so it does make for a great MR. With the miles you get and the minor cost of completing it, can really give you a lot of miles.
I will sit down and calculate the approximate cost this MR will be to include Hotels and plane expenses. That way you can see how much it can really cost. I don't stay in very cheap hotels (there are some that can be found for around $50 per night but I like to include the points for the hotels I need stays for) but the cost is pretty much dependant on your own budget.
I did two MR from SAN - IAD - SAN this year when UA was having the specials to compete with Indy air. I was able to fly back and forth on two MR for under $250 and that was with no hotel stays. I was awarded almost 7,000 miles, not including my 1k bonus and 1,000 points for booking on the web for this amount and it can be done.