Hi
Regarding type variable naming, a few of my more hardware minded friends I've asked to try Haskell often tease me about the opaque type variable names in the Prelude--it seems greater consideration of type variable names in the Prelude might behoove new users.
I think that single letter names are very a good idea for most of the things in the Prelude. 'a', 'b' etc. are good for very general things like the basic classes (Eq, Num, etc) and for parametric functions (flip, (.), etc). I also like the 'm' for Monads of all kinds, but I would suggest to use 'mt' for monad transformers. For collections I think 'c' is nice and 'k' for keys seems to be sort of standard, but I would like to propose using 'e' as generic name for elements of collections, if there are more element types, then 'e1', e2' etc.
Looking through the Hoogle logs, if people search for a multi-letter type name, they are usually getting the wrong end of the stick. People often search for: char -> bool I don't think there is anything wrong with single letter type names, unless you are making your types too complex. Thanks Neil