Thanks to the recommendations on here, I recently started using GetClicky to monitor my website traffic, as well as keeping an extra eye on my adwords account.
Since using it, several times I've noticed clicks that are being charged for on my adwords account, and searches not showing on GetClicky, or for example one search was for "Rug cleaners in Sheffield", and according to GetClicky, the IP was located in Sheffield (unsurprisingly). Now when I checked my adwords search terms, it said the user was in the next town over from me (in South Wales!). I'm not saying its impossible that someone in the valleys was searching for a rug cleaner in Sheffield, but GetClickys version seems to be more likely.
Anyone else got experience of similar discreprancies with Adwords? It's not a lot of money each time, but over a month it adds up.