[johnnyb]

nope the Kindle is now on factory settings again, I reinstalled calibre and cleaned everything, reloaded my books (only the epub files without metadata) and still ... it takes like 5 seconds to load up a dictionary entry, something that still doesnt happen with books converted with Mobipocket Reader, Converter, directly from the web as mobis, an online converter i found and of course not Amazon's own conversion tools (the same is the case if the source file is epub or rtf)...
My only conclusion: the mobi conversion plugin in Calibre is flawed and needs a lot of fixing... I'm not so sure why people claim this is not the case with their files and I myself wouldnt have noticed it if i hadnt tried to read a french book in which i have to look up a lot more vocabulary (and move the cursor around a lot more)... (still, the behavior is also the case with english books and factory dictionaries)...
I don't know if you Calibre guys will want to invest more time in trying to fix that problem, I could upload some of the files in question, could give more detailed step by step descriptions of what I've done (nothing different from what I used to do with my Sony Reader) and you could check them against files converted with Kindle Previewer but you surely know better what to do with your software (which is still a great piece, only useless for conversion for me right now)...

Edit: and btw, all I have described is also the case with News downloaded with Calibre...