I've worked with (and am certified in) Notes/Domino (older versions) and MS Exchange, and they both have their good and bad points.
Notes is a fantastic goupware application, great for shared apps/documents/files, workflow, intranets, support databases, that sort of thing. As a mail system, though, it's clumsy. The security can be damn annoying.
Exchange is a superb mail system - clean, stable and reliable, and damned fast. As a groupware system, it's not there - you need other MS products to make it happen. Security, provided you are running AD, is a pleasure.
Personally, I like the idea of both running in parallel.
I saw this bit from the biased comparison article linked to above:
I'm afraid that's a blatant lie. There's no time-consuming maintenance on Exchange; I run 16 Exchange servers and 3000 users, and hardly ever need to do anything on them; they just sit there ticking along happily. Most issues (and there aren't many) involve Outlook on the client side.