My take on this:
THE GOOD:
I think the conditions are an excellent evolution in the game mechanics. In the past everything was codified individually in a given spell or ability which lead to redundancies. Moreover conditional effects are short-lived which does away with a lot of the pre-combat bookkeeping. Everyone remembers the old buff spreadsheets, but this is largely gone. The short-lived nature does, however, present new bookkeeping challenges (see below). But overall, to use programmer-speak: normalizing your data is a good thing.
THE LESS GOOD:
Most of the problems I see with conditions is in the tracking and timing. Short-lived conditions mean you either have to remember to do a save-ends or end-of-turn type of effect. For me, this is mostly a problem that resides in the DM's chair. It's hard enough to run a bunch of monsters all with cool abilities, and to remember what conditions are imposed on them, AND to remember when / how those conditions end.
IN ACTUAL PLAY:
Long ago I created my own condition 3x5 cards that I hand out to players when they are hit with a condition. Now in late-paragon play, I can't imagine how we'd play without them. Some have suggested using less condition-monsters, but the reality is by paragon level almost every type of monster is throwing out a condition or two -- at least this is my experience with published encounters. We use tokens to track things like quarry, mark, curse and bloodied. Again, I don't know how we would function without these tools. For our group, if a conditional can't be handled by one of those two methods above, it's often forgotten. I'm speaking of things like monster-marking, auras, etc. Lastly there are quasi-conditions which are fire-and-forget. I'm speaking of forced movement and prone. For prone, we just put the mini on its side which is pretty easy to track.
SOLUTIONS?
I really only have problems with the timing. All this beginning-of-turn, end-of-turn, save-ends etc. I just wish it was as normalized a system as the conditions themselves, but I don't really have anything to offer. I would only recommend DMs to use cards and tokens. They help us a ton.