After watching the very informative video on APC about FAA violations I was wondering if there was a statute of limitations???

Since FAA violations are under admin law, no there is not a formal SOL. However, in general constitutional terms you might be able to get a dated violation thrown out based on the "stale complaint" premise.

But there is nothing to stop the FAA from violating you, except common sense.

I remember hearing somewhere it is 6 months from the date of infraction? Anyone else know?

If it is a normal, run-of-the-mill situation and the FAA knows about it, you are PROBABLY safe after six months. This is not a legal requirement, but if the process is functioning normally you should have gotten an LOI or heard something after six months if they are going to investigate.

But if they never knew about the occurrence and found out later, all bets are off. Also if they sat on something for a long time and later decided they wanted to pursue it for whatever reason there is nothing stopping them.

The 6-month stale complaint rule is an NTSB procedural rule appearing at 38 C.F.R. §821.33:
Where the complaint states allegations of offenses which occurred more than 6 months prior to the Administrator's advising the respondent as to reasons for proposed action under 49 U.S.C. 44709(c), the respondent may move to dismiss such allegations as stale pursuant to the following provisions:
==============================

the complaint does not allege lack of qualification of the respondent:
==============================

Not the clearest thing in the world. The cases tend to focus on what is considered " good cause" for the delay and what is considered to be "lack of qualifications" But the way it's been applied generally is that if there was no good reason for the delay, certificate actions will generally go away 6 months after the incident is reported. IOW, you have an airspace incursion, talk to the FAA telephone number you are given, and 6 month go by without receiving a Notice of Proposed Certificate Action, you are probably home free.

But the twists in this hardly give the certainty of a true statute of limitations.

Does anyone know how long the radar/ATC records of daily activity are kept for all the IFR/VFR Flight Following Traffic?

It depends. Unless "pulled" it a fairly short time, though I forget exactly what. It may even depend of the facility itself.

But if there is some action contemplated, they would be "pulled" right away anyway and kept for investigation and enforcement purposes.

So, for example, if you were flying along and heard the magic words, "N1234X Possible Pilot Deviation Advise You Contact City Approach at 123-456-7809," the chances are that the ATC paperwork of preparing pilot deviation reports and the segregation of the ATC audio and track information, has begun.

I think it's 90 days, but of course they will pull it immediately if they have any issues.