Everybody has to like the idea of unlagged. it's in the very name. Use this feature, and all your games will be as smooth as you could want them.
Except, they aren't. With surprisingly low pings (pings that would be tolerable in a "lagged" environment), you encounter all kinds of anomalies.
1) Since things no longer happen in real time, as they used to, it is possible for my fleeing tyrant to die while safely around a corner. This is the first thing everybody notices. In my time, I'm safe, in my enemy's time, I'm not. You see the same sort of thing happen with the roles reversed - a human might be running backwards off a ledge to try to get the hell away from my tyrant, but unlagged gives me a sort of range boost, so my enemy dies because I killed him in my time, even though he was safe in his time. My experience with any other game than Trem is that there is only one timeline as to when things happen, which is in the hands of the server: where the server thinks things are, not where the clients think things are.
2) Random hits. I can't explain the technical aspects of this, but I don't believe I'm the only one to have experienced it. It's most noticeable with the MD - you're taking what you hope are well aimed shots are your enemy, and one of them hits, but you immediately realize you didn't have your sights on the guy. It's like you are shooting at one dretch with multiple hitboxes.
3) Element of balance - The clearest example is the ATCS hallway - you gather a couple of would-be-bad-shots-without-unlagged naked rifles and stand them together, and no dretch can survive the stretch of hallway to attack them. It is my observation that dretch > lagged rifle and unlagged rifle > dretch.
Edit: Related thoughts...
Lagged and unlagged are not one and the same and so cannot be balanced the same. (I think this makes people think that the game should be standardized one way or the other, and since it would be impossible to completely get rid of all the unlagged servers, the way to standardize would be to mandate unlagged.) Personally I don't consider some perfect balance to be important, or possible, therefore I don't see it as something to strive for. We have two drastically different teams, and right now they are not balanced with unlagged or without it. But they are not egregiously imbalanced. The way to say it is the way the Supreme Court integrated schools - "separate is inherently unequal." I don't like unlagged or third party balance. Third party mods are great, but the idea of somebody saying "I have the secret to a perfectly balanced game. download HERE!" is nonsense.
You can't balance the game based off of players, because players themselves are imbalanced. The analogy is chess - white and black are mirrors of each other, so the players decide the match. To REALLY balance Tremulous, you would have to have players who are mirrors of each other (an impossibility) and tweak the teams until you can statistically show (by an infinite string of drawn games) that the teams are balanced. And at the very end of it, after you produce your two separate but equal (IMPOSSIBLE) teams, you hand them to a community of how many thousands of unique players?