The background in the photo makes a massive difference to the file size. Could this be the issue for you Paul when it becomes a problem?
If the photo is of an aircraft against a blank sky you can get away with a large image and the edit will still be way under the limit, whereas if the background is very 'busy' with airport structures etc, then something like 1200 wide can push you over the 1MB limit.
I stick at 1024 for 'security' reasons, so it is never an issue for me - 20D or 40D. But I guess the size limit was imposed by Johan due to technical issues at that time, so it seems to me to be a legitimate question whether this could be reviewed in the light of the brave new world of the rewrite/new servers etc. Once on the site, uploaded photos generally tend to be only half the size of the actual image that you upload - due to the compression applied in the uploading process I assume. But even so, there must still be issues about the size of the database with so many photos stored on the servers - though storage is probably far less of an issue for DM
than it was to a lone guy in a university room.