What’s the best word to get people to click to act?

When we want people to click on a button and carry out an action, there are a number of widely used options for the word or words you put on that button.

 What’s the best word to get people to click to act?

Off the top of my head, there's [Go], [Submit], [OK], [Continue], [Confirm], [Proceed], [Select]. But which of these is the most usable, effective option? [Submit] is problematic for me because it's not plain English and it implies that you are sending something to someone (such as an error report), when in fact you are only sending an instruction to the website. [Continue] and [Proceed] could be confusing if you're not in the middle of a multi-step process. [Select] could similarly be ambiguous if it leads me to think I must choose between options I can't see. So what works best?

I put this question to Jakob Nielsen at London Usability Week. His answer is that [OK] is a good fallback, but can also be problematic too: what actually are you saying OK to? In his view, a button name will be as specific a label as possible of the task at hand. He gave [Add to cart] as a perfect example of this, while also warning that brevity is crucial. So we can see that [Download], [Apply now] and [Buy now] might be usefully descriptive, while [Upload your details to the website] might raise other issues...