I had an issue with a control that looked for pages and displayed them I did this by appending a querystring parameter ?id=1+2+3 (where 1 and 2 and 3 where the page numbers I wanted to display.  I kept getting weird results ie the page that was being displayed was not the one I was expecting.  After a lot of hunting around I realised that the pages being displayed were the pages that were in the pages library with IDs of 1,2 and 3.

I would like to thank Stuart Starrs (www.starznet.co.uk) for pointing out the error of my ways.

http://www.starznet.co.uk/sharepoint/blog/Strangebehaviourinthepageslibrary.htm

The moral of this story - dont use ?id= in a query string unless you want the page in the pages library with and id of x.