I say this having only watched friends play the game but, my stance is that FFXI is much too time consuming and unrewarding to be worth paying a monthly fee for.
Now I've never played a MMORPG before (nor am I a computer gamer) but of all the FF games I've played (7 through 12) this one seems to be the most slow paced of all. The process of leveing up is the longest I've ever seen, and there's the added danger of even leveing down If you happen to die in-game.
I just don't have the time, patience, (or money) to deal with a game like that. But that's me anyhow.