A bit of a haiku here, but several pretty annoying things for the 3.3 betas 2 and 3 for the WordPress platform:
- the jQuery UI libs are named in a different way and persist in an additional /ui folder in the wp-includes/js/jquery folder. Go figure compatibility there – either have to support version checking or to embed them in a theme/plugin (really not recommended)
- jQuery is version 1.7, released just a few days ago. You know, it takes a month or two to have most jQuery plugins, extensions and effects compatible when there is a serious major change. So it could be really hardcore at the end.
- editor changes – some big time changes with editors could cause 2 editors on add/edit pages and some other eventual issues with several plugins
- media API changes – the uploading mechanism has been updated so all file editors, galleries etc are potentially affected