It is 670KB now. When I started playing it was like 50. When will it stop and what gameplay information gets stored?

I've noticed this too. When i completed the game 100%, i made a backup. Then i went playing online for months, and the size just got larger and larger. Of course, editing the teams and adding more schemes always increases it's size. But it's faaar from too big. Some games take 500mb for savegames, and i'm just glad worms doesn't.

it's probably schemes. of course, there is a possibility of a glitch causing duplicate entries. that can cause the size to increase at every save regardless of whether there is actually new data to be added or not.

Everytime you start worms 4 an additional about 4kb (might be less) is added to your savegame file. I have no idea what kind of data is being added but it seems like it is unnecassary. Your savegame file will continue to grow the more you play worms.

Any official word from Team17?

I think it could be the number of games played being stored in there...I remember I tried to hack mine with note pad and it had a lot of my games that I had played listed there...
Like (RobowurmzvsReddawg@RobowurmzSchemeKABLAAMTeamRobo wurmzRoboteamTeamReddawgSuperWormies)etc.
I think it is storing EVERY SINGLE LITTLE GAME YOU PLAYED!
Biiiiiig space!