How Well Do Most OSes Handle Resource Management?

schlika asks: "After getting some troubles with a highly loaded Web server running Linux 2.2.12 I read some infos about its max thread/processes limitation and 'not-so-great' virtual memory management. Could some of you comment such issues with other OS's such as FreeBSD (which everyone says it's better for that task without ever giving explanations), OpenBSD, NetBSD, Solaris, Linux2.4 and others? Please give real world examples/comparisons if possible."