I recently ran into an issue where editing content within a Content Editor web part would cause the following message to appear in the Publishing Toolbar:
The page you are attempting to save has been modified by another user since you began editing
At that point you would have to select "Save and Overwrite Changes" in order to proceed. This would happen any time that you edited a page, provided that you first selected "Edit Page" from the Site Actions menu. If you simply clicked the drop-down for the web part and selected "Modify Shared Web Part", this problem would not appear.
After spending a significant amount of time troubleshooting the issue it was narrowed down to one of the customizations that was made to the master page. The Site Actions menu had been relocated to under the Quick Links menu.
I went back to the default.master page that ships stock with MOSS to try to reproduce the issue. Sure enough, if I put the Site Actions menu after the Publishing Console, I would receive the "page has been modified" error. If I put that Site Actions menu prior to the Publishing Console, everything would work fine.
After a little more than 5 hours troubleshooting the issue, it was determined that simply relocating the Site Actions menu to the top of the page was the simplest solution, however I would like to understand why it cannot follow the Publishing Console, or what needs to be done so it can.