I use them as well and find them very good, but somewhat over-priced for what is offered. I bought an excellent, well made and sturdy pocket diary diary for 2011 (and am currently debating with myself whether to use the 2012 Moleskine diary I purchased, given that I also bought a Letts of London diary for 2012.)
To be candid, quality of the paper used, while good, could be better - and given that I use a fountain pen quite often, sometimes, I find that I have to wait (a bit) for the ink to dry; fortunately, it doesn't bleed all over the page as happens with many products which come with an inferior quality of paper which was one of the reasons I originally bought the Moleskine. I must confess that I like the cream colour - it does beat the bleached white used so much everywhere else.
In common with a number of posters in this thread, I find that a solid diary is very handy for taking notes - and I use one daily. The Moleskine can fit in a back pocket - it is about the size of a chunky wallet - but it is usually in my briefcase, as one cannot use a MBA for everything, and nor do I wish to. besides, there are times when nothing beats being able to take your own notes, at meetings, or simply strolling about.
Actually, the quality of paper in notebooks, diaries, etc has really deteriorated badly in recent years; oddly enough, and perhaps surprisingly, given our disdain in the west for much of what used to be made there, the former communist world makes extraordinarily good paper, which is an absolute pleasure to use for writing - I assume the methods used are somewhat old-time, or less modern.