There are a number of users (couldn't give you an actual percentage) in the various organizations I have worked in that set their resolutions at 800x600 or 1024x768, no matter what the monitor size, CRT or LCD, or resolution capability. It isn't just an age issue, because I have dealt with users in their 30s that do this. It also doesn't seem to be correlated to users wearing corrective lenses or not. With those things said, it appears to be a preference, not necessarily a need.
I think these people have no problem with icons or bold text. I think they want every day text and labels a bit larger. Sans-serif fonts probably help them as well.
Again, this has just been from my observations. I have not interviewed any of these users about why they seem to prefer the lower resolutions. They do pose a problem for application development though - we always want to be able to get more form items or output on the screen!