Since I just declined a group invitation again, a little clarification on the why behind that.
I've been in a few groups a while ago. Followed an invitation, applied for a few others, &c.

I didn't like it.

First of all, my inbox was way too full most of the time. There were nice images among those, but the time it took to clean up was more than I was willing to invest – contrary to the point of groups I haven't found the signal to noise ratio much different from other ways of finding images I like.

Then there is the point that I submit almost all my images under CC anyway. Anyone is free to include them in their group if they want to, no permission by me even required (though I think dA requires it anyway, although that's covered by Creative Commons). So if you want one of my pictures in your group just do so, but don't ask me to select. In my experience I have been a very poor judge of what other people consider a good picture and groups are – ultimately – run by not me.

In any case, I won't start with groups again. This may make it sound like an addiction, but it was more a nuisance. I won't consider joining any group again. This isn't for any elitist reason that I think my pictures are too bad for a particular group or that I consider myself above joining groups. I just didn't like the experience that came along with it.