Thanks, but timthumb will be gone on the next release. I've found that many users just struggle with too much to get the thumbnail functionality working, so I've experimented with a different solution and it seems to be working alright.
About your question on the Featured Image and the Nextgen Gallery: nope, there's no solution for that. I prefer using WordPress' native features than relying on another script / plugin to get the job done. The reasoning behind this is the same as with Timthumb: native stuff generally works well without asking the user to perform any additional actions and so things are simple and easy to use. So, you'll need to set up a Featured Image for my plugin to use it (or select a different source, such as First Image on post or Custom Fields).