[slater]

The company I work at is using it for a CMS.

Drawbacks of it seem to be large initial download (Total initial download for the CMS's files is 1.1Mb, of which almost 900Kb is JS), and some stability problems after leaving it running for a day.

As for the community "problem", in addition to pay-for support, there's a also lively forum and IRC channel.

Not too big a fan of it, imho the benefit of using extJS seems to be a large download, and dropshadow'd floaty DHTML-windows. Meh.