Currently Being ModeratedSep 14, 2011 7:17 AM (in response to Sobeck)
Screen resolutions are determined by your graphics hardware, not Lion per se. However, the display settings were changed on my Mac mini for the HDMI port after the Lion upgrade, and it keeps resizing all of my windows for minimum resolution on startup, so I'd venture to say that Lion has a few bugs regarding screen resolution that are in need of bug-fix updates.
Currently Being ModeratedSep 21, 2011 3:54 PM (in response to Sobeck)
Click on the desktop, then select 'Show View Options' from the 'View' menu, where you can adjust the size of your desktop icons. The maximum resolution of your iMac has not changed because of Lion.