I've done "pair programming" a few times, with (I think) great effectiveness, but (a) it's been in a very specific context, where we each brought substantial but not-fully-overlapping expertise to the task (not pairing a newcomer and an experienced developer); (b) it was an entirely voluntary thing that the two of us decided to do, not something imposed on us by management; and (c) it was for short "sprints" of no more than a few days, not for extended periods.

If it became a required part of daily work in my company, I don't think I'd be around for long.