Is there a public database that show whether a US patent was reexamined or challenged in any other way? If so where is it?
That's a good question. In general you can use Public PAIR to find out a lot of detailed information about issued patents and pending patent applications.
A good example is this is the touch screen patent by Steve Jobs: US7479949. The patent was subject to re-exam and all claims stand rejected in a non-final office action.
The '949 patent provides an interesting example of how to use the Patent Application Information Retrieval (PAIR) system to find the FILE HISTORY for a US Patent. Re-exams are represented in a non-intuitive but consistent way in that system.
First visit PAIR. Once you get past the CAPTCHA you'll see this:
Note that you must select the Patent Number Radio Box and you must use only the numerical patent number without any commas or other characters, i.e. "7479949". The PAIR interface is ridiculously unforgiving... There is also a byzantine distinction between a Patent Number, a Publication Number, and a Control Number or Application Number.
From here you can see on the highlighted red boxes that it is indeed a "Patented Case" (in this case, as opposed to a Patent Application). You can also see that Steve P. Jobs (Palo Alto, CA) is the First inventor. Finally you can see the tab Continuity Data
Click on Continuity Data tab.
This tab refers to other members of the same Patent Family, in particular Continuations of the subject patent. From here you can see the Parents and Children of the subject patent. For example, you can see that the entire patent family Claims Priority to the inventions described in a US Provisional Patent Application filed by Steve Jobs 9/6/2006.
You can also see the Children of this subject patent. Here is where it gets weird. The USPTO represents re-examination proceedings as if they were children of the subject patent. You can see here the re-examination proceeding referred to in this fosspatents article as child application number 90/012,308, which is pending.
If you click through to that child "patent application" (actually the re-examination) you get a screen like this:
You can see that this "patent application" is of the type "Re-Examination", its status is waiting for an Examiner Action following a Non-Final Action (in this case, the claims stand rejected but we'll see that next).
Click on Image File Wrapper to dig into the detailed discussion between Apple's attorneys and the USPTO.
Wow, that's a lot of dialog between the USPTO and Apple! But you can see on 12-03-2012 as indicated the result of the Re-Examination. This is the same date referenced in your article. Apple has the right to continue arguing with the USPTO (as long as it continues to pay additional fees) but for now this is where the patent stands:
Click through to the document Reexam - Non-Final Action
In this PDF file you will see the current status of the Re-Examination for Patent 7,479,949, which is that all claims stand rejected.
It's not easy to navigate the PAIR system but worth learning if only to see the detailed arguments between the applicant and the examiner. Examiners often spend a lot of time and effort analyzing applications. It's a tough job!
Using PAIR, as Micah's detailed answer shows, is definitive and by far the best way to look things like this up.
Not definitive but easy, if it has what you are looking for, is Google patents. It keeps getting better and as of a few months ago has a "Legal Events" section at the end of some patent documents. In the case of the infamous:
Method of swinging on a swing US 6368227 B1
It shows that it had a reexam that left all claims canceled.