I use Multisite a lot. Even for stand alone installations the super admin function alone makes it worthwhile, especially for client's sites I take care of.
I've also found it realy useful for running a small network of local community oriented sites. With the type of hosting cost centres we have in SA, we often pay a noticeable extra amount for a few more databases and another GB of storage, no unlimited databases, no, unlimited storage, no unlimited anything here in sunny South Africa.
Multisite makes running such websites more affordable in SA.

Over the years I've seen WordPress drop quite a few good things, sometimes in favour of poorer ones. The change of Tiny MCE was a good example.

I think if Multisite was dropped, and no plugin available to replace the functionality I think I would finally abandon WordPress as a client website platform and switch to Drupal which has a solid system of managing multiple sites. All Drupal's layout and content display flexibility, and the rock solid security of Drupal core are way ahead of WordPress in that regard, the only real problem is building a client's ability to get to grips with the content creating tools and methods.

Just when WordPress seems to be closing the gap on things Drupal does best- content sorting and display, and the layout flexibility introduced with WordPress blocks they start talking about messing around with important stuff..... grrrr....