I like warlock and I've had fun with the ability myself. But TBH it isnt always useful a lot of times, there's not always room (remember its a spread) to use it without hitting the party and good luck using it when the party is already engaged in melee. But yeah, if you've got an enemy caster or a group in the back you might be able to hit them with it.
As others have said, it is possible to teleport out of it-you can still use Verbals for V only spells OR command word items. Of course if you've a cleric in your party, or you're a multiclass like my own Cleric/Warlock/Eldritch disciple you can drop a Quickened silence over the area as well. It is certainly possible to have psionic abilities in items as well, which generally only require a mental command.
You may have more than one caster in the enemy group and spread them out so they are not so close together-if the warlock grapples one, the other will have warning and may dispel it. FURTHERMORE-either caster could have a Ring of FoM, or the
Freedom Armor property from MiC. The wizard at this point could/should also be flying if ceiling heigh permits, I know the Warlock will (or at least ought to be.)
ALSO-if you like, you may House Rule that while the warlock can cast his Evards as much as he wants, casting a new Evards ends the first, the same way as it is with Nightmare's Made Real from CoM.
How do people normally deal with say, WEB?
http://www.d20srd.org/srd/spells/web.htm
(Albeit entanglement does not negate somatics, it requires a Conc check; and the fighters would have an easier time cutting the wiz out, than beating the grap on the tentacles and THEN making an aid/assist to the wiz. Also mind you Evards only grapples you once, if you are in the area when it is cast, or if you enter it. Breaking free keeps you free until you leave and THEN re-enter.)