Linkedin, the site asked me to provide a list of my skills. I didn't think this unusual because knew that LinkedIn was intended to be a site to help people build their career (as distinct from Facebook which is more intended to be more of a site for people to enjoy themselves and relax). However, since I was not seeking out a new job, I didn't pay too much attention to what I filled in there.
Recently I started getting notifications from LinkedIn to say that one of my contacts on the site had "endorsed" one of my skills. I never actively sought out these endorsements and so I was somewhat intrigued to know what was going on.
About 2 weeks ago, I got a LinkedIn connection request from someone I know and when I approved the request I was presented with a list of the skills this person claimed to have and was asked to endorse them. Since I knew this person to be reasonably competent, I clicked the "endorse" button beside some of the skills. Then the site asked me if I wanted to endorse more skills from other contacts. It began showing me an apparently random set of people/skill combinations and prompted me to either click on the "endorse" button or else click on the "next" button to see more choices.
In general, I endorsed contacts' skills when I had a reasonable knowledge that the person did hold the skill that they claimed. I sometimes declined to endorse someone's skills either because I did not know them very well of because I knew their abilities and I did not rate them very highly (two very different situations). Although I spent a while reviewing skills, I abandoned the endorsement exercise before I had a chance to review most of the people/skill combinations so many of my colleagues were not endorsed by me due to lack of time/motivation.
I suppose the bottom line is that when you see that the skills a person's LinkedIn profile have been endorsed by someone else it gives you a slightly increased confidence that the person does indeed hold the skill that they clam, but if there are no endorsements for their skills it does not necessarily mean they are not skilled.