The article is a bit overstated. Just because the worker process may be recycled, and therefore all in-proc state is lost, doesn't mean that in-proc session state "does not work." It works as advertized. If this is not acceptible to you (i.e., online retail where state = shopping cart = $$$), then don't use it. If it is (a forum, a blog, etc), then use it and don't freak out.
I could sit here and claim that out-of-proc session state doesn't work because (unless you use sql 2k5 correctly) there is no event fired when the session state times out. Its just a limitation of state models. Pick your poison.

I would agree with yesthatmcgurk. The feature works as advertised and that's how I've used it.