From my experience I can tell that it's almost always possible to find better alternatives for Microsoft products and technologies. It seems like the only people who use MS stuff are those who don't care about what they have at hand.
Let's say you have $200 a month to spend on email and collaboration. You have no IT staff, no programmers, and you have no IT experience of your own. What is better than (hosted) Sharepoint + Exchange?
If you are in that amount of money you are better off with Google Apps free hosting. One day of Exchange expert for setup or problems is in the hundreds.
Google Apps isn't even close to being better than Office+Exchange+Sharepoint. You can get hosted Exchange and Sharepoint for $15/user/month, with no setup fees.
I need an alternative LDAP directory with an integrated Kerberos Key Distribution Center and a modern usable user interface. Any ideas?
Or those for which it would cost a substantial amount of time (and therefore money) to learn a new stack of technologies when they can use existing skills to build stuff more quickly.
Learning new things always costs time and money, it's called an investment and in the case of getting off the MS stack, it's well worth it.