Hi Donncha ... I was looking at your website and saw the link to 'ismyblogworking.com' and tested it out on my site only to find that my blog is "BROKEN" .. uh-oh ... so I checked it and sure enough, instead of my site, I see a bunch of what may be termed 'gobbledy-gook' ... yikes!
So I turned off caching and reload my page, it looks okay ... WHEW! I turn caching back on again and I'm returned with more gook ... so I start looking at settings ... 'compress pages' ... hmmm ... could that be it? I turn that off and see what happens. So far so good ...
I am using 'Cloud Hosting' at VPS.net .... perhaps this is another of what is meant when in the plugin admin screen it says "Compression is disabled by default because some hosts have problems with compressed files" ..?
Anyway i hope that was the problem ... scared to take a lunch!
Thanks again for all the help.