I wrote some time ago about what monster roles actually exists in 4th edition D&D, and how they don’t always match up directly with the printed monster roles. I mentioned that the Lurker role seems almost totally non-existent in the monster manual when I perused all the heroic-level monsters. Since many monsters are listed as “Lurkers”, I’ll explain this more thoroughly.
According to the description of what a Lurker is supposed to be, it is supposed to be a creature that launches a big attack every few rounds, withdrawing in the meantime through stealth, mobility, or some other defensive ability. This sounds like it could potentially be an interesting kind of monster, so I put in my descriptions that this is what a Lurker is supposed to be. It would be possible to build a monster that works this way mechanically. However, almost none of the monsters in the monster manual actually work like this.
Some of the monsters are capable of acting in this fashion - for instance, they can turn invisible and hide between attacks. However, they have no reason to act like this. The description for lurker is generally indicates that while they are hitting and running, their allies are fighting at full intensity. It is extremely disadvantageous to have one monster attack once every 3 rounds instead of every round. While he can hide on the other rounds, this is not very helpful to his side because the players can simply target a monster which is not hidden. Basically, it is almost as if the monster is unable to attack 2 out of 3 rounds.
In order for a monster to want to spend an entire round not attacking, it would have to get a huge advantage to compensate. Many monsters do get small advantages - for instance, if they waste a round becoming invisible they can gain combat advantage on the next round, and the opponents will be forced to attack a tough soldier next round instead of them. But this isn't even close to compensating for the massive disadvantage of losing an entire attack.
Now, it is possible for the game master to ignore the correct tactics for the monster and have it make hit-and-run attacks just to make it feel like a cool lurker monster. In some cases, this sort of GM control can be effective at creating the proper atmosphere. However, such a monster is not really a lurker, but rather it is a coward. Pretending that a coward is actually a lurker only works as long as the characters don't catch on. Once they do, it can be rather annoying. D&D is a tactical game, and if the players think that a monster is a lurker, they will naturally want to foil its ambitions when they have a chance and try to corner it and force it to fight straight up. Unfortunately, if the monster is actually a coward rather than a lurker, this is the worst thing the player can do because the monster becomes much more powerful when it is forced to fight straight up. If the players realize this, it can really disrupt the suspension of disbelief and the general atmosphere of the combat.
GM: The cunning bandit strikes from behind, then disappears into the shadows to avoid reprisals.
Players: Oh good, now we can beat on his buddies in peace and deal with him later. Maybe we should try to avoid throwing any area attacks in his direction - we wouldn't want him to feel threatened and come fight us. We definitely don't want to cast our "reveal hidden enemies" spell.
In theory, however, it should be possible to create a monster that is a true lurker. One way to do this would be to give the monster low defenses and an extremely powerful attack with a recharge roll. That way, it might be a better idea for the monster to withdraw until he recharges his power, rather than fighting with his ineffective at-will power and probably dying before his main power is recharged. In order for this to work well, the rechargeable power needs to be much, much stronger than the at-will power, not just a little stronger. Another, more heavy-handed approach is used in the Imp, the only true heroic-level lurker I could find in the monster manual. The Imp has a special power which is more than twice as strong as his basic attack, and it only recharges when he uses his lurker power to turn invisible. Hence, he is strongly encouraged to alternate attacking with turning invisible. And while invisible, he probably has nothing better to do with his move action than sneak around the combat and try to prepare for a mischievous surprise attack - in other words, to act exactly like a lurker is supposed to act.
All of this discussion relates to the idea of having lurkers in the same fight as normal monsters. If you fight nothing but lurkers, the dynamics of the fight change completely, and it is much easier for a monster to be an effective lurker. If all of the monsters are extremely good at disappearing on the same round so that the players have no targets at all, this can be an effective tactic even with some of the "lurker" creatures listed in the monster manual. For instance, I found that the young Black Dragon is nearly invulnerable inside his zone of darkness, so he can afford to sit there and wait for his powers to recharge. As long as he doesn't have any allies for the players to attack, this seems like a reasonably effective tactic. The only problem is that I found this was rather boring, it wasn't very exciting for the players to withdraw to a safe distance and sit around twiddling their thumbs and throwing ineffective long-range attacks while they wait for the dragon to come out and play again. The fight was more fun when I had the Black Dragon give up the lurking concept and just go fight the players.