500d uses rubbish non-standard frame rates - it's video is deliberately hamstrung to keep it in it's place (in Canon's hierarchy). 20fps @ 1080p is useless if you ever hope to do anything even vaguely serious - the other two resolutions (720p and 640x480) are basically NTSC - and not even correct NTSC - so also problematic if you hope to do semi-serious stuff (although not as problematic as 20fps).
550d = brilliant, the full range of broadcast standard frame rates, it even has 50fps (for over-cranking / slow motion).
Video:
500d uses rubbish non-standard frame rates - it's video is deliberately hamstrung to keep it in it's place (in Canon's hierarchy). 20fps @ 1080p is useless if you ever hope to do anything even vaguely serious - the other two resolutions (720p and 640x480) are basically NTSC - and not even correct NTSC - so also problematic if you hope to do semi-serious stuff (although not as problematic as 20fps).
550d = brilliant, the full range of broadcast standard frame rates, it even has 50fps (for over-cranking / slow motion).
Video-wise absolutely no comparison.