19/01/2010: I think this plugin didn't work after the 2.9.1 upgrade
I have loaded the 'Adhesive' plugin, which controls sticky posts on the home page and in categories. I haven't investigated it fully, but it seems capable of keeping a post on top of the home page even if it isn't the newest. This is why I wanted it i.e. it keeps a particular item (e.g. a Welcome post) at the top of the front page. You may want to alter its content from time to time, but it stops new posts pushing it down the page/screen, preserving a little bit of structure.
This plugin was not reinstalled when the site was upgraded.