Oh, one more thing. This is non-related but if your going to look at the above issues you may as well be sure that you have assigned a primary domain through webmaster central as well.
Websites can have more than one URL. (e.g. http://www.bluewidgets.com and http://www.bluewidgets.co.uk). If you have been around for a while and people are linking to you they could be linking to either URL. By designating a primary it gets 100% of the above benefits. Go to Google’s Webmaster Central and in the tools section designate one as your primary. Do a 301 redirect on the non-primary page to pass on any back link juice, PR and authority that the page has to the primary page. Internal navigation needs to be checked to be sure all links go to the correct version as well. Bad navigation is common, especially with websites constantly being populated or worked on by many individuals. Pick one and use it throughout.
GaryTheScubaGuy