I'm wondering if my experience is normal or if I'm doing something wrong. It seems like it takes forever for my ads to start running when I do a placement campaign on AdWords. And unfortunately sometimes they just never will start even when I bid what seems like should definitely be enough. It's experiences like this that makes me want to just throw in my hat and not deal with AdWords. I just don't get it. It should be more reactive to what you do. If I pay enough to run an ad on a page, it should just show up right away, damn it!
Ads on 'placement' get reviewed both by google and the publishers of the site in question - http://adwords.google.com/support/bin/answer.py?hl=en-uk&answer=81867 - it may be that the sites just don't want your ads :-(
I've found that you really need to add a lot of sites to get traffic this way, and sometimes it can take up to 4 days to start seeing traffic on placement ads, and unfortunately it appears you will never get placement on some websites.
Not forever, but it could take few hours or days. I keep saying - reviewing time.... If you really want to do AdWords, learn how to deal with them. Start your campaign one day earlier than it is suppose to. After one day, if your ad didn't appear - and probably they will not contact technical support; they will review it and your ads will surely run. Patience is a virtue .