Recently I have been watching a lot of WordPress TV. I came across this interesting video about Optimization of WordPress. Ben Metcalfe is one of the founders of WP ENGINE and gave an amazing talk at the WordPress Philly 2011.
Here is a short list of the Blacklist of WordPress Plugins from the Ben Metcalfe talk.
Take a look at the list, and there is another post on the blacklist page that explains in quite a bit of detail why these plugins are removed off their servers.