If the projected market is global, but the patent is only issued in the US, what will the cost be to cover other countries?
Is there still time to file abroad in desired markets?
The rest of the world works on the basis of "first to file", so if someone invented well after the US inventor, but filed first in the country in question, it would be quite hard (not impossible) and expensive to contest the foreign filing.
Cost and means cost of enforcement
The PTO issues a patent but does no enforcement. Protection and enforcement of the rights implicit in the patent are up to the inventor/holder: Does the holder have the means to enforce its rights? No cash to pay for litigation is about good as no patent.
If a company is granted a permanent irrevocable exclusive license to the patent by the inventor, the holder is the one that has to protect it through litigation, unless the right to prosecute infringers is granted along with the license, which normally isn't since the licensor is expected to protect the patent rights as consideration for the royalties received. Does the holder have the ability, financial means and will to protect the patent rights? If not and the company does not either, it may have no means to prosecute infringers and in practice have no patent at all.
How "real" is the patent?
This is the question that seldom seems to be considered. In "Patents: what do they mean to you" I referenced the debacle of Research In Motion (RIM the maker of Blackberry) whose issued patent had one claim invalidated years after being issued.
Another interesting case is that of so called "bogus patents" as this "Must Read" case reported by ReadWriteWeb.com:
The notorious U.S. patent 6,411,947, a broad "method" for automatically classifying and responding to email inquiries known as the Firepond/Polaris patent, has finally been invalidated after 12 years on the books. (continue)
The warning here is: if it looks to you to be too easy, too obvious to be patentable, have an expert check the details, not just validate that the patent is issued. If it does not quack like a duck, it may not be one regardless of the stamp put on by the PTO or it may be so only for a short while.
Are patents useful?
Of course they are. They certify to a good degree the novelty of an idea if not to its economic value. By virtue of the prior art research done, they attest to the difficulty of finding competitors. Competitors could well exist that have prior art but never bothered to file a patent and they could come out later as they did for RIM.
Should inventors file them? Of course, but with the awareness that they grant no explicit protection. They only give one the right to spend money in litigation to protect the rights implicit in the patent.
Should investor value them? Certainly, but, in my view, subject to the above considerations and making sure that due diligence includes looking carefully under the hood.