[ynniv]

"Facebook" is also pretty generic, but when you have enough well paid lawyers these things matter less.

Also, it is very unlikely that Facebook is attempting to benefit from 53's brand. Facebook wanted to call their product something descriptive, and the names collided. Compare this to any name involving "Facebook", which likely is attempting to benefit. Outside of a directly competing service, it's unlikely that the name of a product would include the word "Facebook". This makes "Facebook" less generic and more enforceable than "Paper".

[ig1]

Facebook was completely generic. Facebook used to be term for the paperback student profile books that universities produced. Facebook the website started as an electronic version of the paper facebooks.

[ynniv]

Facebook was completely generic.

Yes, Facebook WAS generic. They would have had a difficult time enforcing their brand from the start. Once a brand becomes a household name (which is admittedly a vague metric), the rules are different. See Apple, Windows, Sun, Sharp, Digital.

[ig1]

The standard isn't "household name", but rather "acquired distinctiveness" which in the US is defined under the terms of Section 2(f) of the Trademark Act