Comment by rwmj

Absolutely. Two things I remember (from back in 2005) were:

Campaigns defaulted to worldwide. You've got some naive new user selling for example hand painted dolls to a UK audience. They sign up for AdWords, and get a huge influx of visitors, yet nobody is buying. Why? Because the website doesn't and cannot sell to all these new US and worldwide visitors. The thing is the seller is an expert in dolls, not SEO, and has no idea what is going on.

You can set a daily limit on ad spend, which is nice, but it means that your advertizing works really well for that niche midnight - 5am visitor profile, but doesn't actually bring in local buyers who are awake at normal times. Again, the naive AdWords users usually have no logging or stats (and if they do they wouldn't necessarily know how to interpret it) so they don't understand what is going on.

I hope Google have fixed these two things, but I'm sure there are plenty of other traps.