The Weaver grows to become one of the most powerful Creep classes(not saying much, considering half of them are incredibly lackluster), at least in terms of 1v1 ability. It tends to be fairly popular, although not nearly to the degree of Wargs, as the initial ranking to 6 can be quite brutal. After that it gets a LOT easier and more fun.
Rest of your questions others have answered.
[LEFT][COLOR=#ffffff]Morlenil Barkolomew Turmuz Shurz Gruubluk
Posting in white; so people can read my dismal ramblings easier.[/COLOR][/LEFT]