[rtiangha]

If you're importing any of the Kindle fonts, you'll need to check all of them to ensure the weights are consistent between the different types. I just did this myself; almost all of them have problems. Not hard to do; just tedious. Works fine by default on Kindle (and the Adobe renderer and maybe even koreader, I believe), it's just Kobo's kepub renderer that's picky.

In fontforge, go to Element->Font Info.

Under the PS Names section, make sure the Fontname matches one of Kobo's preferred styles (ex. Fontname-Regular, Fontname-Italic, Fontname-Bold, or Fontname-BoldItalic), and that the Weight is set to "Book" for the regular and italic versions, and "Bold" for the bold and bolditalic versions.

Under the OS/2 section, under the Misc tab, make sure the Weight Class is at "400 Regular" for regular or italic, and "700 Bold" for bold and bolditalic. Finally, under the PANOSE tab, you can either clear all the options by setting them all to "Any", or just make sure that the Weight is set to "Book" for regular and italic, and "Bold" for bold and bolditalic.

Then go File->Generate Fonts, select "Truetype" to save as a ttf (or Opentype to save as otf, but the Advanced Font Options patch only works on ttfs) and then Generate to save. Optionally, before you do, you could click on Options in the save dialog and uncheck TrueType hints (as some people say that no font hinting looks better on eink devices) and check the "Old style kern" option to attach a kern table to the font which the kepub renderer needs to properly apply kerning (although the only Kindle fonts that don't already have a kern table are the monospace ones).