Does Google (and others) differentiate between keywords starting with a capital letter vs. all lower case? ex: promotional products vs. Promotional Products
No there is no difference, you can use any of them. This is because google and other search engines are not case sensitive.
no. it's just a preference of people in making there keywords capital. maybe to make it more visible or noticeable to others.
yes, I think miner difference in caps & small letter because Google is sensitive for keeping keywords.
It's the same, tried this with german keywords and in german lots of words have capital letters, but for my keywords it did not make any difference getting them higher.
Google Searches are not Case Sensitive. That means if you search for Poker, poker, POKer, POkeR etc... all will generate the same results for you. Its not at all a problem if you write your keywords in whatever case.
My vote also goes to capitalization being irrelevant. Pay more attention to your phrases and plurals though. Stella Roberts is 100% spot on.
Although capital are not important you might want to use them in your keywords on pages to attact customers to a link. For example pokerface or PokerFace The last one is more visable and more people will click on them. So for being more visable you might want to use more capital letters in your words.
As all said Google is not case sensitive... capital and small letters are same ...not only Google all the well known SE are not case sensitive
Searching keywords is not case sensitives. So you don need to worry about it. it wont affect your SERP.