I would say that the pluses would be obvious Oceans.

As far as negatives go - at a guess, a younger man can expect more than an older woman could give him. There's also the fact that as they both age - the woman will physically age at a much faster pace.
If the physical ageing isn't a problem - then the emotional problems can kick in. As we get older, most women don't look for the thrills or the topsy turvy emotions that a younger person experiences and dealing with these could be quite exhausting.
I believe these relationships can be quite enduring, but it would certainly take a lot of work and patience from both parties and in some cases, the male may be looking for an extension of his mother, which could be difficult if there are children who are also competing for her attention.
In the short term - I would guess that these relationships can be exciting, stimulating, refreshing and fulfilling - but over a period of years, could become quite boring.