If you’ve been deploying and removing lots of InfoPath forms over a period of time, be sure to check the ‘Solution Management’ section of the Central Administration site. Each InfoPath form gets assigned a GUID and is installed as a .wsp. It seems after you remove these forms it does not always remove the wsp, so you may have a solution management page that looks like this:
It’s not a bad thing but might be good to give it a cleanup on a regular basis! To remove the wsp, just click on the name and click ‘Remove Solution’.