I understand that the one-touch "Live Preview" button locks up the mirror, as on the 1DIII
Personally never bothered me. We have some of the best tools ever. Always a few quirks.
Yeah, I've been using stop-down / mirror lock-up until recently, but you need to nit-pick them to death otherwise they get way too complacent. Fortunately Nikon's doing that for us now ...