Hi MbWannabe, I love working back and forth between Maya to Motionbuilder. And the newer versions seem to be getting better and better with fbx. The absolutely fastest way to in MY OPINION (Iam just a student, but I do alot of playing around testing) to rig a Character for your needs is in Maya go to HUMAN IK/SELETON generator. Instantly you have a skeleton with all the bones ready for Motionbuilder. Then you place that in your characters Mesh and adjust all bones to fit your Character. Then what I do is use the auto skinning Maya script to automatically skin the Character quickly. Link to that info is below.

you can see youtube here ...
http://www.youtube.com/watch?v=EklzamltEgM
and download here ...
http://www.creativecrash.com/may...racter/c/pm_heatweight--2

http://area.autodesk.com/for...otionbuilder-much-easier/

also, I like taking Daz studio characters (hundreds of free public domain Daz/Poser characters on web) and exporting them from Daz Studio via FBX in to Maya. Then in Maya quickly rename the major MB bones and then export to Motionbuilder. Then instantly characterize. Then I just export the fbx ANIMATIONS back and forth from MB to Maya and Maya to MB. Its just too easy. Here are few of my tests ....

http://www.youtube.com/watch?v=8VXboOWrS4c
http://www.youtube.com/watch?v=BtPdgBQjYOw

by the way I also have a lot of fbx motions. I have collected several thousand free public domain fbx motionbuilder stock motions from the web over the years and now using Microsofts Kinect box (only $149 at Target) and the Motionbuilder Brekel Kinect hack to make my own like fbx motions.
http://www.brekel.com
http://www.youtube.com/watch?v=a3CvIg0VE1s

lots of fun!