eWeek had one of the coolest lab tests I've seen in a while last week: they tested portal applications for speed on different architectures. This is exactly the kind of testing I'd do in my little lab if I had the resources.
eWeek tested JBoss on Windows, Plone on Windows, XOOPS on Windows, Plone on Linux (SUSE), XOOPS on Linux (SUSE), JBoss on Linux (CentOS), Liferay on CentOS, and Sharepoint Portal Server on Windows. Their results were mixed: .Net had the highest throughput per second in KB, Windows JBoss the highest number of transactions per second, J2EE/Liferay/Linux the highest hits per scond, and JBoss on Windows the lowest page load time. .Net and Windows JBoss were among the fastest portal applications, but the various LAMP flavors did OK, especially if you did something to speed them up. (Like using Zend Technologies' PHP accelerator.)
The main point of all this testing did not indicate that one portal architecture necessarily better than the rest. If your organization has expertise in a specific portal area, then that architecture will work for you. The key is that whatever architecture you choose is what matches your business.
Information Technology is changing, as always. What matters most is not the technology -- it's your understanding of your business and how to make that work faster and cheaper. IT and IS are just tools for your business.