Larry Augustin, founder and chairman of VA Software, has written a very clear editorial at sandhill.com on why applications are the next wave in Open Source adoption. Augustin has a strong background in open source from his Linux days and is involved in several open source application companies. Clearly with the amount of VC investment going to open source startups ($400 million in 50 startups over the last 18 months) there are others also placing bets in this area.
While VCs have been known to overinvest in speculative areas (and that's an understatement!) you have to wonder what is driving the investment. Augustin goes through a well thought out investment thesis to describe what he believes will separate the winners from the losers. While Augustin may not be completely unbiased in his writing, it's still a good analysis.
I've also included two other links that give more insight into Augustin's views on open source business models.