Binary package hint: mythtv
Recently, a new minor release of MythTV was announced, version 0.20.2. Feisty contains an svn checkout after 0.20.1.
For North American users, guide data was previously provided by Tribune Media Services through a service called Zap2It. Starting September first, this service will be discontinued. A non profit organization, Schedules Direct (www.schedulesdirect.org) has been formed to replace Zap2it for guide data to all North American users. Schedules Direct unfortunately requires an update to the new MythTV release due to new servers being used, and guide data being stored in the MySQL table differently. With this release there is an ABI change, meaning that all machines using MythTV will need to be upgraded to have a version with the same ABI. This goes for plugins as well, all of mythplugins will need to be using the newer 0.20.2 release too. Archive wise, since this isn't a major version bump, no NEW binary packages will be necessary, libmyth-0.20 will still be used.
The format for guide data through schedules direct is different than Zap2it's previous format. All shows are stored internally with a longer series-id (presumingly) for future support of more possible shows. After installing this version, the MySQL tables will be updated, and guide data will be translated over to the new format. Unfortunately, due to the ABI change, just applying the patches that do this is not feasible. This would provide a false assumption that these packages worked with packages using the old ABI, which isn't the case.
I would have to rank this as being a very severe problem, as without guide data, a MythTV box is useless for North American users. At this point, the only options for Feisty users would be to upgrade to Gutsy (which had 0.20.2 uploaded recently) and use the testing release, or to compile the packages from source themselves. It's hard to estimate how many users will really be affected, since popularity contest doesn't provide statistics on people's locale. The install number for mythtv-common is around 7.5k, but again there isn't much information about how far back that goes.
As for changes other changes involved, you can view a changelog between the 0.20.1 minor release 0.20.2 at the MythTV wiki: http://www.mythtv.org/wiki/index.php/Release_Notes_-_0.20.2
The 0.20.2 release is developed in a branch separate from trunk. All of the changes that have been put into it have been backported out of trunk, and should be considered stable. Since no major 'features' have been introduced, I would expect the risk for regression to unaffected (non North American) users to be very low.
Attaching a diffstat of the upstream tarballs.