Has it been a (relatively) steady path or have there been wild swings over time? I'm not UPS club but I started AdSense in June 2003 and have seen mostly stable earnings over the years.
I've been to several AdSenee in Your City events and think networking with other publishers is just as important as the suggestions from the AdSense team.
One interesting takeaway from those events: most of the top earners have old, established sites. I've not met any publishers at these events that have sites that are less than about 4-5 yrs old, most are 8+ years old.