I've done pair programming. With the right partner it is productive and produces better code. The person at the keyboard is at a disadvantage because the partner has more "think time". Anyway, I found it pleasant.

The KEY problem is management. My partner always wanted to type so we ended up with me doing the thinking/review while he worked out the syntax. When we got our performance reviews my partner got a raise and I got a bad review. My manager believed that he did all the work and I just sat around talking.

Beware the 'review' trap...