I know I'll get criticism for this, so let me start by saying it is not an attack on Spyderco - I think they're a great company, and honestly if everyone owned as many of their products as I do, they would make Apple look small by comparison.
That said - I do feel people here seem to treat intellectual property protection as if it were some inalienable and never-ending right. Patent laws were not created to provide someone with eternal exclusive rights to their own inventions. If society guaranteed that you could not use anyone else's idea unless you had a legal licensing agreement with them to do so, then society as we know it wouldn't exist - we'd still be in the Stone Age. Patent law exists to benefit society by:
1) Protecting the ability of the originator of an invention to exclusive profits from it for a reasonable length of time, that compensates for the effort they put into the invention, and motivates others to be inventive.
2) Ensuring that after that reasonable length of time is expired, the invention is freely available for others to use. That is why patents have to be published.
A typical patent in the US is 20 years. So if Spyderco had patented their hole when first invented, the patent would have expired by now, and it would be available for anyone to use. However, they didn't patent it, they instead chose to trademark it, perhaps because trademarks don't expire or maybe because it would not have been judged sufficiently inventive to qualify for a patent. They are therefore using trademark laws for a purpose for which they weren't intended - the thumb hole was designed as a functional feature, not as a trademark or logo like the Spyderco spider. I understand why they would want to do it, but I don't feel companies should seek to exclude others from using a functional feature in perpetuity through the mis-use of trademark law. If it is a technical innovation, get a patent, and accept that when the patent expires, others will be able to use it. This is part of how private companies contribute to the public good.