The need for supplemental condition testing and splitting the pattern matching among the where clause and the boolean guards is considered very cumbersome by some.
Yes, it is. But that was only an artificial construction, meant to work in general. I wouldn't do it that way really. When an individual problem is reformulated in the correct monad, the entire program becomes much simpler.
the (<-) notation isn't overloaded at all really, any more than it is in list comprehensions. <- always means monadic bind. it is fully general in 'do'. restricted to the list monad in list comprehensions, and restricted to something like the exit monad you mention in pattern guards. They are all consistent uses of (<-).
No, they are not the same. Bind in a list comprehension translates to the exact same bind in do notation. I cannot think of any translation of pattern guards for which the same thing is true. For example, in my construction, pat <- e translates to pat <- return (e). That is a very significant semantic difference. -Yitz