I would appreciate any thoughts you may have about the use of Grass Carp to control unwanted waterplants in lakes. Any information pro or con will be useful. Thanks.

Check out pondboss.com, if you haven't already. Tons of discussion on that forum.
Also here is a link to info on the TPWD site
http://www.tpwd.state.tx.us/landwater/water/habitats/private_water/gcarp.phtml#facts
A permit used to be about $75. Grass carp from a hatchery are between 5 and 10 bucks each, about 10 inches long. Different pondmeisters have had different results using grass carp. If you feed your bream and catfish with pellets, the carp may go to eating that and not touching the aquatic plants you want to get rid of.Its kind of a gamble.

Here is a link from TPWD. Grass carp won't control all types of vegetation so it would be a good idea to identify what you have and see if they are know to control that type of vegetation before you get some.

http://www.tpwd.state.tx.us/landwater/water/habitats/private_water/gcarp_intro.phtml

I have been there and done that. I now use Aquashade in my pond and it works wonders.
http://www.aquaticeco.com/index.cfm/fuseaction/product.detail/iid/1481/cid/4036

Take a look at Martin Creek and Lake Cherokee and look what the grass carp has done to those lakes. A good fertlizer and lime program will balance out the weeds.

a good friend of mine bought a place that had some in his 15 acre tank.The 1st yr he had it the veg was thick around bank the 2nd yr we started noticeing huge carp rolling in the shallows.This place was primmo bass fishing .By the third yr the tank was a mud bowl .Nothin but huge grass carp starveing with every thing else.

I think the lesson is to use just enough grass carp and to be patient while they do their job (several years, probably). If you try a "quick fix" with too many grass carp, you'll wind up with a mud bowl after they eat up all the vegetation.

Also, a grass carp can and most likely will grow to 40-50 pounds. Most fish will not reach such a large size in a small body of water but grass carp will. 1 or 2 in a small pond is all it takes.