Not that I normally repond to trolls/flaimbaits, but I've actually spend about half my career (5-6 years) with Domino, half with Exchange (7-8) (and a bit with Groupwise - 1 year) -- so I'm think I'm in a reasonable position to be able to talk about the two intelligently.
I spend more time in a month managing Domino issues than I do in a year or two with Exchange. It's not that Domino doesn't work, it's just that it's 'death by a thousand papercuts' - literally. With Exchange (and to it's credit, groupwise as well), I more or less don't have to touch it after initial install and config. A couple changes hereand there over the following months, and DONE. With 8.5 FP1, I spent months tweaking the crap out of config files, and it took the better part of a month just to get DAOS working properly without crashing (on a completely fresh install). And then just simple maintenance over the following years is long and painful.
Despite IBM's perpetual propaganda, most big companies are moving off Domino, for mail at least. Domino is half decent on the groupware side, but for all but the big fortune 500 companies, it's just too much of a pain for simple mail and a bit of groupware. Honestly, Domino is like SAP - if you have a whole giant-ass department of people to manage it for you, it's not half bad - precisely because you have a giant-ass department of people managing it. For anyone sub-enterprise, it's a waste of time and money.
It's not even any cheaper, either. I recently worked for an SMB (150 users) who was on domino (7.0.3), but on the fence about staying with them. So we have IBM quote us 8.5 (with Sametime, and a few other small pieces), and it comes out to be almost double what Exchange plus sharepoint came out to. And this is AFTER we grilled them and grilled them for discounts. All the while IBM is telling us that "SMB is actually their bread and butter clientele". Both on price, complexity, and infrastructure, Domino just doesn't compete sub-enterprise.
The only reason the company was on Domino in the first place is because the owner liked 123 back in the early 90's, and thought Domino would be a good idea.
Or do I need to elaborate further?
P.S. - Let's not forget about 99% of the user base that HATES the client, and BEGS for outlook.