Using wpmu as a basis for a web design business platform

I have been running my web design business for many years and now am almost exclusively WP based. I have been using whmcs with individual cPanel accounts for customers.

My question is what are your honest thoughts on using wpmu as a basis for running multiple web sites for customers for various businesses?

Practically none of my customers ever access cpanel and only a few do their own maintenance.

I love WPMU so far so I would like to know if there are any pitfalls with putting all existing and new customers straight to WPMU?