Google Adwords?

I got a voucher recently for £75 of free advertising on Google Adwords. I wasn’t really planning to use it, because I think Adwords is quite expensive for someone like me. I don’t exactly do a “hard sell” on this website, so even if I get extra traffic, probably only a small percentage would actually buy my book. I can’t really see how I’d make back my money (apart from of course during the free period, which only lasts a few weeks).

But I just thought I’d ask if anyone has experience of using Adwords, and if it might be useful for me after all? Do let me know if you think I’m missing out.