> We could even convert all bitmaps to little-endian, since 
> only Mac uses big-endian and we know that nobody important uses Macs. 

Shouldn't we support both endians?  If an image opens with big-endian
bitmaps on a little endian machines, couldn't we automatically correct
them on startup?  Sure it will take time, but if startup time is
important, just save your image and the bitmaps get saved in the native
endianness.  I suppose you might need a class for each endianness
(LittleEndianBitmap, BigEndianBitmap).

- Stephen