Whilst trying to determine if this blog was performing badly (or not) I came across this great site – monpage.com
Its free to use and will provide a graphical representation of the availability of servers and the responsiveness of webpages.
I configured it to monitor this domain, another domain hosted with the same provider and the same virtual machine which is also a WordPress blog but not using a cache plug-in – markbingley.com who’s a friend of mine and then for comparison I added Jerrys site which is a Domino blog hosted by prominic.net.
Here’s the results for yesterday (22nd February 2009):
As you can see having a Cache plug-in for WordPress is definitely a requirement
I am not sure the Graphs tell the whole story, when I navigate Jerrys site it seems allot more sprightly compared to this site so YMMV.