I saw a book recenty, called Linux annoyances for geeks which looked quite interesting. Thing is, are books really worth it or is it better to stick to online sources as probably more up to date & relevant?

I think that linux books are useful if they are general, which basically covers command line, networking, good practices.
For immediate help or problems, I use online sources as it is quicker and more likely to be up to date.

There are a lot of books out there that are just not available on line. The information might be if you can find it.

Sometimes I like to read before bed or when I'm flying so I would find it hard to give you a choice.