Ok, a few emails on the list that didn't get in here:
First, the new JAI ImageIO release candidate supports GIF, so users could just use that. But it is RC, and actually didn't work in my tests.
> About the support in the java advanced imaging. It's release
> candidte thing. Either we integrate the GIFOutputStream class - which
> works perfectly into org.geotools tree, so no additional jar is
I was thinking that it was more than one class. I agree, I think we should just integrate it into the tree. Though I think org.vfny.geoserver.responses.map.gif is a more appropriate place than on GeoTools, as I don't think GeoTools so much wants to deal with out put formatting. If they end up wanting it we can move it, but I think it's fine on GeoServer for now.
I'll test this out and roll it in when we move trunk to 1.3