Do I need to worry about thread safe methods?

[Recursion]

7. This is the importance of the static keyword

That's the main advantage of Java and C# from a developer's perspective: the VM forces declaration of static members and methods, so that you can see exactly where you need to worry about concurrency.

If you're sure that there can be no two concurrent calls of any static methods (and anything that accesses a static variable is a static method), then you're fine. I'd actively prove it to myself, though.

In terms of why you care, the normal case for bugs is that a method stores some kind of recordkeeping data in a static variable. User A and user B try to write and read that at the same time, and the result is inconsistent. Inconsistency is a bug, and will eventually make something explode.