>I don't see authors for FAQ/Downloads section. I can not sort it the way I want. I can not see, which category it belong.

PMFJI

Category has been removed since two weeks. This does not apply anymore.

>I also don't see a usage of Search by UserID. In order to do it, you have to Search for this user first, copy his/her number to a clipboard, then search.

For some it is. It depends on what you want to achieve. Some day, maybe you'll have a use for it. Otherwise, just use what you have a use for.

>It would be much more convenient to search by user First/Last name combination.

That is a good suggestion. I'll take note of it.