I ran autogas in my Cessna 150 (carbureted O-200 engine) for several years.  I had the following observations:

1)  The engine had a slightly greater tendency to collect carburetor ice.

2)  When leaning the mixture, the "peak" was "softer".  Since I had no EGT gauge I just went by leaning to peak RPM and then enrichening slightly.  On Avgas the peak was "sharper", i.e., little extra leaning caused the rapid dropoff in RPM.  On Autogas it was "softer" and the actual peak was slightly harder to discern.

3)  I used to run ARCO-brand gas, until one of my friends chastized me about "that cheap crappy gas that he wouldn't even put in his car".  I then switched to Exxon.  With sufficient effort I could almost imagine that the Exxon gas ran slightly smoother.

4)  Autogas smells horrible compared to Avgas.  (No, I don't sniff it for fun, but if I did, I would definitely choose Avgas...)

- Rob Wolf