Well I’m assuming that a client that owns 600 properties will secure appropriate hosting, so whether it’s one or 600 installations is rather immaterial. And it’s rather presumptuous of you to say that the MSM solution “was not designed for him” especially considering that to the best of my knowledge you do not have any personal experience using MSM. Arden has not provided enough details about the sites to allow any of us, myself included, to determine if it’s his best option. He’s worked with ExpressionEngine long enough, though, that I wager he has weighed the options and knows what he’s doing.
And I do not wish to derail Arden’s topic with a discussion of your fifty sites, but yours is a rather different situation. Your “sites” do not have independent weblogs and templates. There are clever ways to make it seem that they are, through wise use of URL segments and such, but the layer of separation is a facade (capable though it may be), and the facade doesn’t extend to site preferences. Take EE and CI as an example, though, and you’ll see that having actual unique template groups is a must. They both have a ‘bug_tracker’ template group, but each has dramatically different needs. To accomplish that without MSM would result in incredibly messy templates full of conditionals and situational tags that would be burdensome to create. And I can’t even imagine how difficult it would be for a developer who was not involved in the creation of a site to suddenly inherit it, which happens often with many design and development firms that use ExpressionEngine. I’m tragically off topic now, and I apologize. If you wish to continue a discussion of the difference between running multiple sites with and without MSM, please start a new thread in the General discussion forum.