One of the great things about WordPress is that anyone can develop a plugin for it to extend the functionality over the basic core.
The bad part is also that anyone can do it.
Not all plugin developers are equal and some bad plugins are definitely part of the WordPress ecosystem. A lot of them aren’t maintained at all.
When you search for plugins or WordPress.org or using Bing or Google, there are a couple of warning signs to look out for.
Incompatible With Most Recent Version of WordPress
Unless a version just came out this shouldn’t happen. It’s the definition of not being maintained. It may still work, if you really need it make sure you test it before taking it live.
Unresolved Support Tickets
It’s the support tab on WordPress.org. If downloading from other places check if they even offer support on GetSatisfaction or run a forum or something. Some developers offer support on Twitter.
This should also be obvious, not all reviews are trustworthy, use your judgment.
Again the nice part is that anyone can contribute to the WordPress community, so nothing is stopping you. If there is a plugin that is out of date you could always take up maintenance. Chances are someone else has built something that will work and is being actively maintained.