Hi Mario,
The support for MHT isn't too bad right now, though I see that the Chrome version doesn't include images and Firefox support may end in November (with a lot of things).
The idea of MHT is certainly good. Being able to save whole web pages in a single file is very useful. The only thing more useful might be a way to view epubs embedded in a TW document. I've found an epub viewer for FF, but alas it doesn't work as an embedded viewer (it's more of a stand-alone application).
Thanks,
Mark