Hi Marcus, Thanks for dloading this and appreciating the work(coz mostly people just download the plugin)... :P
Ok, now for the things you asked. First of all, I did have a plan like that in my mind. But then I thought that if I integrate it with the WordPress Uploader, then the other images that it creates(resizing it etc etc) might also be optimized by TinyPNG. This way, it'll lead to a hell lot of wastage and might just cross your limit for the max no. of images for you account. There is one way to stop it... but a lot of mind will have to be put into it and right now I am having my exams(so, I didn't really start working on it)
Secondly, for the JPG support, I planned only on playing with the compression level of those photos. I might put jpegtran to use but I then again, like I said, I am busy with my exams.
Don't worry, I'll definitely start working on it soon. More and more features will get added, but I feel that will take a little time(maybe by the end of Jan).
Thanks again, Please rate the plugin. :)