Since updating to Safari 5.1.4 (as far as I can tell) I'm now getting a serious crash when I try to view cinema listings at Showcase Cinemas website. When I click on a any of the links for the cinema listings Safari hangs (beachball of doom) and appears to hang the entire system (can't force quit and trying to freezes Finder including the Dock). Have to shut down by holding down the power button.

Mac Pro (early 2008), quad core running Mac OS X 10.6.8 (fully updated).

Is this just something on my Mac or is this reproducible on other machines?

First thing I'd check is whether other browsers suffer the same issue.

If they don't then Safari does appear to be the problem. Try turning off plugins, JavaScript and Java in the prefs and try again. If it continues to crash, suspect something on the page you're visiting. You can send bug reports to Apple from the Safari menu, and it may help to send them the URL that's causing the crash.

EDIT: I'm running 10.6.8, Safari 5.1.2, with Flash and ads blocked. The Showcase site seems to work normally for me.

Works fine in Camino which suggests it's a Safari issue.

Probably not related to your problem, but Safari 5.0.6 (on Leopard 10.5) always crashed when I closed a window with a PDF in it - I tracked it down to the fact we have Acrobat Professional 7 installed and this places a plugin into the "Internet Plugins" folder, here:
Macintosh HD > Library > Internet Plug-ins >

Removing that file, and turning off the option to view PDFs in web browsers in Acrobat's preferences, seems to have solved the crashes - it still displays PDFs in the window, but now uses the OS X built-in capability.

Adobe strikes again! Although, to be fair, it is an old version of Acrobat by today's standards. I could install the free Adobe Reader, but to be honest it works well now without the Adobe plugin. We still need Adobe Acrobat Professional for editing and saving PDFs, so I can;t bin it altogether, but at least it's not affecting Safari any more.

I'd check any Safari Extensions you have installed as well.

The only extensions I have installed are AdBlock plus and DIVX (and they are the latest versions). I was't trying to view PDF's either.