This from a fellow (and soon to be ex-) MovableType user: he just upgraded to 3.0 but still found this note from his hosting service in his inbox:
You need to find an alternative to your MT as its running very high in the process list. MT has a lot of flaws in process management and security and causes a lot of problems on the server.
This week looks like I’ll take a poke at migrating to WordPress . . . . performance was always a problem with MT 2.x and if they’ve not fixed that in 3, why bother?