Verbed brands
No, verbs are almost never capitalized (see Edwin Ashworth's comment for the rare cases when they are). I suggest a good article on verbing brand names on The Economist:
So to google became to search on the web, to facebook meant to look up
or contact someone on Facebook, and to skype covers calling someone by
VoIP telephony.
Among photographers, meanwhile, to photoshop is common currency for
what you do to an image after you've snapped it
'Genericided' brands
As Edwin Ashworth pointed out, I missed the first part of the question about noun capitalization.
Normally, if a brand noun is used as a generic noun, it is not capitalized, but many companies insist on capitalization, to prevent a process called genericide which is described in a very interesting article:
"Are You Guilty of Genericide?" on Daily Writing Tips. The article deals with capitalization issue, and the point is:
- brand owners insist on capitalization but fail to achieve this
- people tend not to capitalize and this trend wins
It is disputable whether capitalization is a mistake or not. While brand owners object genericidal effect, dictionaries accept brands as generic nouns.