Weapon Expertise and Implement Expertise are a pair of feats presented in Player's Handbook 2 that grants you a +1 bonus to hit with weapons of a specific group or a specific implement, respectively. Now that the feat is out of the book, we're getting the usual gripage about how its too good to the point where some are proposing that it should just be freely doled out to everyone just by virtue of being a player character.
Is the feat "too good"? I think that depends on one of two things: either you think your character has a sub-optimal attack bonus, or you are really into character optimization.
I think its really handy for multiclassing characters. For example, I wanted to take Kobal into warlock so I could aim for that infernal captain thing, but decided not to because it would be virtually impossible to actually hit with the warlock powers. Implement Expertise would make things a bit more viable, and I might just do that. Her attack bonus with a trident is really nice (+12 at level 8), so I'm not worried about that: I prefer to build characters around an interesting concept as opposed to optimized builds, anyway.
The game math is getting tossed this way and that, ignoring the fact that at higher levels you can get bigger and bigger situational bonuses to your attacks, especially from leaders. Going off of my warlord, bloody ending doles out a +2 power bonus to attack against an enemy, there is a level 7 encounter attack that grants a power bonus, and at level 10 I am going to take instant planning since it will give everyone in a close burst 5 a +4 power bonus to all attacks. Technically I can give out differing bonuses to my party members as I see fit, but that's a pretty steep benefit by itself.
At higher levels where people claim the math falls apart, there is a warlord stance that grants both you and an ally a +2 power bonus to attacks (among other things). That lasts for the entire encounter. I found these while perusing the new warlord powers in Martial Power. Granted, I'm sure there are more in the Player's Handbook, but I decided to go with what I had handy (someone left it on my desk after our last session). I didn't even bother scouring magic items, other leaders, or other feats to see what came up.
Checking the math in a vacuum produces some despairing results. I think that, on average, you need to roll like a 15 or better to hit most things at level 30. Someone posted that the required number was actually like, 14 or higher, but its going to depend on many factors like race, class feature, weapon/implement, etc.
However, none of this accounts for stuff like combat advantage, leader bonuses, or bonuses from secondary stats like fighters getting to add their Dexterity modifier to some attacks (or as a penalty to defenses), and the chances really start to fall into your favor.
In the end, both feats are really nice but not necessary. When my players have trouble landing attacks its because they either roll for crap, having a hard time working as a team, or I've found a way to divide them up with controller monsters. The fact that they scale up makes them more appealing and can allow for more flexible character builds. This is good, but again I dont think everyone is going to automatically take this feat with every character.