I believe perspective employers look for you on LinkedIn. Plus if someone who knows you professionally is trying to find you and offer you a job, it is where they search. I'd say, yes, be on LinkedIn. But it is more like a 65%-strength yes, not a 100%-strength yes. Your presence on LinkedIn is unlikely to hurt you, and may help.

Plus LinkedIn is a good place to search for jobs. At least my kind of jobs.

Besides the picture, are there any other LinkedIn mistakes of note?