Is Google AdWords Any Good?

Just received £75 of free Google AdWords vouchers in the post. I thought I might as well give it a try… but is it actually any good?

I do a little bit of freelance web design/web development in my spare time – so I don’t want to be flooded with work. I’d also like to focus on the London area (for now).

Does anyone have any ideas or suggestions on how to best use the £75?

Any advice would be much appreciated!