Examiners do sometimes look at non-patent art. Art that is disclosed by the patentee will almost certainly be reviewed. If the U.S. patent is the U.S. phase of a foreign (or PCT) patent, then the U.S. examiner will usually have access to the Foreign search report, which, expecially if it is the one done by the European Patent Office, will be far more likely to contain non-patent prior art.
I'm not really sure what you are asking for here. If you are the patent applicant, there are reasons for and against doing a comprehensive search. If you do a comprehensive search, and find nothing, then you are probably in good shape to obtain your patent -- or if you do find stuff, at least you know going in what issues you might run into in trying to get a patent. If an applicant wants to make absolutely sure that his or her patent gets issued, then a comprehensive search of both patent and non-patent art will be the best way to try and draft an application that can get issued.
However, if you do a search, then you are obligated to disclose anything you turn up to the patent office. This could be an issue if you find art that is "close" but not exactly on point. If you disclose it, you risk the examiner taking a more expansive view of what the art covers than you think is correct, and therefore you might have to overly narrow the scope of your patent to get around any rejections. If you don't disclose it, and you later end up in litigation, the fact that you didn't disclose could be grounds to invalidate the patent entirely.
If you DIDN'T do the search, and the examiner failed to turn up the "close" art, however, then you might be able to get a broader patent issued than if you had found and dislcosed the art. Such a broader patent might then be challenged in a later court case (if the defendant found the "close" art), but by that time, the burden of proof shifts from the examiner's burden of "preponderance" to a higher standard of "clear and convincing." In other words, once a patent is issued, it takes more "proof" that the "close" art really covers the patented invention than it would if the art was uncovered at the pre-issuance stage.
It's a complicated problem. Many agents and attorneys will counsel their clients to not do any significant searching before filing the patent. Of course, most clients will already know of some relevant art, and that art must be disclosed, but oftentimes it is best to let the patent office do their job. If a patent issues, and art is found to exist that is close, then it's up to the challenger in a court case to try and prove up a case for invalidity.
All that said, it is ALWAYS a bad idea to fail to disclose art that you know about -- it is better to be over-inclusive than under-inclusive when disclosing art to the examiner. But the applicant has no duty to search for prior art, only a duty to disclose what they already know -- and oftentimes, the best approach is to let the patent office search and see what happens.
A different approach may be taken for a particularly price-sensitive client who may be unwilling or unable to risk the application fees on a patent that might not issue -- in that case, it would probably be better to do a search to determine whether or not it is even worth filing an application in the first place. But for corporate clients, usually the advice is to NOT search, and see what happens.
I'm not sure if that answers your question or not.
