I've been using Apex for quite awhile. Tried installing MIUI yesterday, and...well, I'm glad I did a Nandroid first.
The initial install seemed to go fine. Restored from TiBu and suddenly MIUI was force-closing constantly, in, I think, Android Core or something. I'm willing to do some research when my phone glitches up, but not when I can barely do anything without a dialog box popping up.
I'm not blaming MIUI in particular...I didn't SBF or anything first, though I did do all the formatting and such. Not sure that that was good enough. I also use Go Launcher and had restored that...not sure whether that would have any bearing on the situation.
MIUI looks beautiful; I was pretty disappointed that I couldn't get past the errors long enough to appreciate it.