Matt announced today at the 2011 State of the Word that plugins and themes are now hidden from the search results (on both WordPress.org and in the plugin/theme install screens) if they have not been updated in two years.
For plugins only: Older plugins that are still compatible and secure only need to have their “requires” and “tested up to” version numbers bumped. If you do this, actually releasing a new version of the plugin is not necessary, so leave the version number the same.
DrewAPicture, 
Ramoonus 5:30 pm on August 15, 2011 Permalink
isn`t 2 years a bit long? I always stop using plugins which haven`t been updated for 1 year.
Andrew Nacin 3:16 am on August 16, 2011 Permalink
It’s a start.
Jeremy 3:20 pm on August 16, 2011 Permalink
Might there be plugins out there that are so good and really basic that their utility spans greater than 2 years?
It seems that you would want something more to go off of in addition to the last modified date.
Andrew Nacin 10:32 pm on August 16, 2011 Permalink
We looked at the old plugins with the highest download counts and saw nothing that caught our eye. Ultimately, if a plugin author can’t update just the “Tested up to” version, then it’s pretty safe to consider it abandoned. The “Tested up to” values for such plugins are no higher than 3.0, and most are far worse. Otto and I are going to poke around the data and see if further refinements can be made, though.
Pasta Maker 8:04 pm on August 15, 2011 Permalink
Why 2 years and not a shorter period? From what I understand, many wordpress plugins/themes are not really secure and can be easily hacked. Is that true?
pavelevap 5:44 pm on August 16, 2011 Permalink
Old plugins should be also hidden from tags archive on WordPress.org?
Andrew Nacin 10:33 pm on August 16, 2011 Permalink
We’re not there yet — it’s just a pilot with search.
Mark 12:15 am on August 17, 2011 Permalink
Rather than just hide plugins I think it could be useful for them to be listed somewhere for new would-be authors to get inspiration and learn.
DrewAPicture 6:20 am on August 22, 2011 Permalink
Agreed. Though they’d be hidden from main search, it would be nice to still be able to search/browse them elsewhere .Forks could/would happen.
Adam 8:36 pm on August 17, 2011 Permalink
I think this is a good policy. You get rid of plugins and themes that may not work with the newest flavors of WP and it causes less problems. Thanks!
-A
WraithKenny 6:33 pm on December 14, 2011 Permalink
Is this still a two year limit, or is it now a “tested” version?
WP-reCAPTCHA has disappeared (I assume it was marked abandoned), but it looks like it was updated 8 months ago, but was only tested up to 2.9.1. It looks to be a truly abandoned plugin as the authors site is gone, yet people still use this plugin (even if they have to patch it themselves).
Any news on the adopt-a-plugin program?