I will also point out that one does not need a registered trademark to have trademark rights in many countries, and this is certainly the case in the US: the issue is that trademarks are a protection not just for the owner, but almost more primarily for potential consumers; it is effectively a protection against people using familiarity and naming to confuse users into affiliations that don't exist. The concept of a trademark then only requires demonstrating that in your field (as trademarks are always scope limited: if one came across a laundry-mat named Knol it would not be the same issue) the name carries expectation: that people would recognize it and associate it with a specific party.

It also must be stressed that it is not sufficient to have a disclaimer: the user even getting to your website to even see the disclaimer is effectively already under false pretenses, and not everyone reads those messages anyway. If anything, that you feel the need to have such a disclaimer is good evidence that people are, in fact, being confused by your naming. I, for a concrete example, am only on this comment thread because "oh, I remember Knol... I am surprised they are trying to reboot/revitalize that project", and would have read a ton of these comments under that vague premise had it not been for this top one making it clear "no, this is not Knol". This is just such an egregious example of what you can't do with identity :(.