Yes indeed you can add comments but when you do the very same search again it's only you that can see those comments, it's like a little reminder of what the website contains, whether you like it or not.
You can also promote a site you like to the top of the search list for the next time you go looking for the site,but again this only reflects your searches.
I have tried it and was impressed. Sometimes you search for something and the same sites come up on top even though you know they have not got what you were looking for because you have been to that site before, so you can demote them from future searches.