I've run LWP's on Droid Mod, Cyanogen and Ultimate Droid ROM's in several versions of each. I really can't say I notice a lag with any of them, per se, BUT the LWP is a power hog. So the LWP is fine if you are not going to be far from a charger. If it is going to be all day away from power, then you better get a spare battery or two, or don't run the LWP. I really liked the Earth Rotation one, but it is 5.5 or so MB big and sucks up power like the Borg assimilating a civilization. It is a personal choice on what you need out of your phone I guess. Then there there is what seems to be quite a variation in Droid to Droid performance. So some may well run them better than others.
Anyway I decided battery life was higher on my list than a fancy LWP. You won't really need the extra power untill sometime when you really do need it. Even if Earth Rotation Live is kinda cool.
Just like which ROM is best, you won't know if LWP's are for you or not until you try some and see for yourself.