The Series B round was led by Accel Partners. Benchmark Capital, the lead investor in SpringSource's first round of financing, also participated. Word on the street is that the valuation was very pleasing to the team there.
I didn't think much about the Covalent acquisition when it happened but now that Iona is going away, SpringSource is the one-stop shop for Spring, Tomcat and ActiveMQ along with their new Spring Application Platform.
Good for the Spring guys for figuring out how to monetize Apache-licensed projects while building in secret sauce to sell their products. The subtle shift from free software to open source shouldn't be underestimated. Just selling support is not a sustainable business model.