Well I can look back to AdSense as far back as the third day it started for all of us. That was about mid-June, 2003.
Yes certain friends had been mentioning it would becoming available to the great unwashed masses of the rank and file Webmasters. Not just those chosen big players. I adopted my traditional "wait and see" attitude.
On the third day I was "strong-armed" by glowing reports into replacing my Amazon rotating SSI ads for an AdSense trial. I was confidently told, real time reporting would tell me within 24 hours whether it was a good or bad decision.
Within the first four hours live, I had earned almost one months Amazon income. Obviously a no-brainer decision.
Facts most of you will perhaps neither believe, or might churn your stomachs over:
Fact #1: The last time any of my sites were content updated in any way, was about twelve months BEFORE AdSense was even invented - strange but quite true. Haven't really written a new page since about July, 2002.
Fact #2: The biggest, and only "AdSense impacted" change I have ever experienced in over ten years, was way back when they tightened up the click area down to a click-able link. For those who can remember, again strange but true.
Fact #3: Excepting for the impact of #2 above - AdSense over the years has produced, as a "generalisation", constant CTR and constant EPC figures - when looked at over a prolonged period.
I always ignore day to day, week to week, or even month to month volatility.
Fact #4: The only impact upon my earnings, whether it be AdSense, Amazon, Commission Junction or others, has been purely down to loss of traffic over the years, more pronounced in recent years. Not in AdSense itself.
Many factors are at play here, not the least Mr. Googles Zoo in recent years. Linking sites from my peer group in my genre have also disappeared as many of us pass away, this equates to loss of direct traffic. Since AdSense was invented, I estimate the number of competing sites in my genre has exploded at a rate exceeding the number of new people searching the internet for my topics. No doubt for other genres as well.
I am consoled by remaining friends with the expression - "Imitation is the sincerest form of flattery".
Fact #5: Many may bitterly disagree with this next statement, but if there were no AdSense, nor any internet advertising - most of you wouldn't have web sites.
Mine came about 16 years ago by pure accident, when trying to explain complex technical explanations requiring schematics, formula etc. Impossible to do in an email discussion forums back in those days. I created my first web page in 1998, it still exists, and as far as I know it is still the only web page of its type in existence. Think of a topic like:
"Left handed, blue and green striped, pink polka dot topped, widgets for right handed people suffering from arthritis and a heart condition"
AdSense has been a fun ride over the great many years for me, it continues to remains so, it has given me a very generous supplementary income in my retirement since 1998.
ALL: Think of all those things you would have done, or would do, if you were in my shoes?
I would do none of them at all, I never made my sites for AdSense. Indeed my sites already largely existed even before Mr. Google existed.
If I were prepared to invest the time you might, I'd go back to my old day job as a consultant, and charge obscene sums of money - assuming I even cared.
My sites exist to teach, not to make money. NO, I can say I have never been adversely affected by AdSense, nor its policies.