While I have not used MC's in MBT, I have used them to good effect in WWII.
I like to use them in a vanguard/scouting role. The trick I find is to dismount before being hit. I've even gone as far as having them dismount every turn as they move forward. Their main job is to either give me forewarning of the EN LOC or to move into important objectives using their speed and hold until the Main Body can get there.
Since being able to dismount MC units their lifespan on the battlefield has increased greatly. MC's also if in the right spots make great MEDEVAC units to get badly mauled squads to the rear areas. Bumpy rides vs. being dead are a pretty good trade off I think.
Bob out
