I recently changed from a Canon Powershot G3 to an EOS350D
The main changes I noticed:
- Kit lens on EOS350D isn't very good. It is a marked downgrade from the G3 - both in terms of zoom range, and in speed. I'm not familiar with the A80, but I would guess the comparison will be much closer.
- No LCD preview - I'd become accustomed to using the LCD for composition, and it was quite convenient in some circumstances.
- Self-timer button rests directly under where your right thumb goes - I was caught out a few times by that, before I learned.
- Bigger. G3 would fit in a jacket pocket at a pinch. No chance of getting a 350D in there.
- Canon's bundled software is just as bad, but more bloated.
- Walking past the shop with the L lenses in the window has become a trial of willpower.
- Sensor on EOS350D is much better - I was scared of using ISO 200 and 400 on the G3. I accidentally shot a whole card at ISO 1600 on the EOS350D and didn't notice by looking at the pictures - only found out when I checked the image data.
- Better autofocus - more capable in low light, and seems more accurate - with the big advantage that you can see what it is actually focussing on (a little spot appears in the viewfinder). Very useful if you're doing macro shots.
- Much better shutter lag, generally better responsiveness, fast continuous shooting, no power-on lag, can carry on shooting after buffer memory is full - just not as fast. G3 would stop until buffer had completely emptied.
You can see some pics in my sig: with the ones accidentally shot at 1600
here