Alright... I've managed finally to update to 4.1 - FINALLY!
here's how:
first I flashed the 4.0.0 from greekmaster's pastebin, then applied the script to undo the "crappy screensaver hack" included in the partition (which I really urge someone to fix & re-upload)
updating OTA kept giving U006... the bin file it downloads was about 20MB. after some searching I found a Chinese blog, and through the magic of translation I found a link to
the official 4.1 bin from Amazon (he just mentioned it, how updating using it fails if you've installed SS hack)... they say curiosity killed the cat, but it updated my Kindle!
The official Amazon bin is about 40MB... so I downloaded it to try it, maybe just maybe it'd work. sure enough it did =]