Load any CMYK image created with Photoshop and watch the colours. They don't
match with the real colours as The Gimp doesn't understand the Photoshop CMYK
setting (I work with CMYK Euroscale coated).

In Photoshop there is a menu with many different colour standards to chose
between (RGB: Adobe RGB, Apple RGB, ColorMatch RGB, sRGB IEC...  and CMYK:
Euroscale Coated/uncoated, Japan Color, US Sheetfed...) and in the Gimp I can
only choose "RGB". This makes Gimp totally unusable for graphic design involving
feedback between the printer's people (CMYK) and the web' people (RGB),
specially internationally. I had to give up using it professionally because of
this although all the other functionalities are great!
I understand that GIMP follows only the standard but I think this is not
appropiate for real-life designers who have to deal with many copes using tons
of different software...
Anyway big congratulations for your work. I could never imagine that the Gimp
would be so good in 2 years (1->2 switch)!