i currently am using a user-unlocked iphone. it has given me no problems whatsoever, and i am happy with it.
yes, updates are usually delayed by a few days, maybe a week. it's nothing to worry about. half the time, i don't even bother updating the firmware until it's something i really like.
the only thing to keep in mind is that each time you have to update the firmware for your user-unlocked iphone, you will have to reinstall any extra stuff you have downloaded, like cydia add-ons, winterboard settings, etc.
overall, i'd say that the user-unlocked iphone is still very reliable with no major drawbacks, especially if you're using it to save money on your carrier's plan.
cheers,
-Dustin