Excuse me ... i got these 6 webheads ... running only on open source software and all six of them showing the following uptime (and yes, they are under constant load, and i should introduce two more webheads *grin* but well, servers aint cheap and management rarely likes to spend money on new hardware)
www1:~# uptime
19:06:49 up 350 days, 16:07, 5 users, load average: 3.00, 3.00, 3.00
Also the loadbalancer, the mail and database servers, all running on open source software with similar uptimes. But we also have these two Exchange servers running which wont stay online for more than one month since there are constantly new hotfixes to be installed, the machines to be rebooted and we can be lucky if all our management remembers to "archive" their outlook emails every few weeks, otherwise they are in trouble (since outlook wont work anymore) and that means i am in trouble pretty much regulary just because of crappy M$ software.
I usually spend about 35 hours a week managing problems with M$ bases services and just about 5 hours on doing some updates on the open source driven services.
So who is more reliable? Ask Google and Akamai.