How can I speed up the Open With menu?
There is a free utility called Open-With Manager that helps you clean out the unnecessary apps associated with certain file types:


  Open-With Manager lets you edit the list of file types a given application thinks it can open. This is most useful with regard to the Finder's "Open with" context menu; and it also affects the way applications behave when you drag files to their Dock symbols.





  Behind the scenes, Open-With Manager works in a way that's quite similar to Service Scrubber. And to be perfectly honest, Open-With Manager is in fact Service Scrubber's well-hidden, slightly older twin brother. That's why the restrictions detailed for Service Scrubber in this blog entry apply to Open-With Manager as well. When running on Mac OS X 10.5 or later, Open-With Manager will not edit signed applications.


I use this on Snow Leopard, but I haven’t tested it on Lion. Also, it may take a while for the Open-With menus to reflect the changes made in Open-With Manager, so try waiting or just reboot.