This seems like a strange acquisition. VMWare makes money from selling virtualization and VM management software; spring is just a set of popular java frameworks. maybe they're trying to enter a completely different market?
But this is a very interesting acquisition. I don't think many people would have ever dreamt of this team-up.
I haven't used it much in a couple year, but I would not consider Spring lean software in the least, as stated. Standard package comes with quite a bit, but even at it's leanest IoC I'd consider Google Guice leaner (and prettier imo). Certainly better than the old EJB specs though.
Homepage link - http://blog.springsource.com/
Post link (appears to be down at the moment) - http://blog.springsource.com/2009/08/10/springsource-chapter...
It's basically a move into cloud service offerings, so that they can move up the vertical chain - build, run and manage.
I thought it was a little strange at first, but it's quite exciting if they can bring simple hosting and scaling to Java apps, in the same way Spring has made enterprise development easy with Java.