Springer Science+Business Media, which includes assets from Bertelsmann and Kluwer, is preparing for an IPO in 2007 at the latest, according to IWR.
With Derk Haank (ex Elsevier) and open access advocate Jan Velterop (ex BioMed Central) among their ranks, this could highlight the differences to Reed Elsevier. Springer partly uses the Open Access publishing model (thanks Stevan Harnad), whereas Elsevier only allows bareboned Open Archiving. It will be very interesting to see more details from Springer (margins, how many authors choose Open Choice over traditional publishing, etc.). Springer charges authors $3,000 for Open Choice publishing (Elsevier acknowledged it would need to charge the same to make it viable - and then chose not to enter the Open Access field - yet!).
There is an interesting article on Open Archiving at the icWales site. Stevan Harnad on his blog discusses the opportunity cost of not fully embracing Open Archiving.
One last detail: I tracked the number of Open Access journals, as listed by the Directory of Open Access Journals. It went form 1525 in April 2005 to 1763 today. Compare that to the number of journals at market leader Elsevier (1800) and runner-up Springer (1250). Of course, many of the renowned titels still reside at traditional publishers.