Does anyone here take Ninjutsu? And what is it like, practical? Usefull?

Most of what is called ninjutsu is actually koryu jujutsu. For example, the Bujinkan curriculum teaches a mixture of taijutsu. The mixture is composed of three ninjutsu and six jujutsu schools, with jujutsu making up pretty much most of all the unarmed fighting techniques.

All depends on the teacher.

The thing to understand is that certain Ninjutsu Schools were lost to disuse or banned and faded away. There are only 3 left in practice. Although the Ninja always incorporated Budo arts into their own fighting methods and permeated them with Ninjutsu, so that they worked together.

I thought Ninjitsu was focused around stealthy movement techniques, etc. and didn't itself contain any combat techniques.

It does have some fighting kata too, for example Santo Tonko-no-Kata of Togakure-Ryu shows how to escape from a fight.

They weren't just assassins, many of them were ronin. Stealth is part of Ninjutsu, but it's not the focus of it. They were pretty fierce fighters, but since many of them were spies they did have to be sneeky. From what I have read they were warriors first then became Ninja, so they had Budo training prior to their Ninjutsu training.