Does anyone have experience with using any of the retargeting platforms with their Magento store that they could share? We're interested in doing some retargeting to bring customers who have browsed back, but aren't sure which provider to go with. Any pros/cons/gotchas would be super helpful, as well as any data on efficacy. We're a little concerned that simple "hey, come back to our site" retargeting is a waste of time and money, but would love to hear from someone that's implemented it on their store before we jump to conclusions.
Use Google Dynamic Product Ads.
Install the google analytics universal tracking code with the walkthrough here if you haven't already done so: https://stackoverflow.com/questions/22229312/universal-analytics-could-not-track-transaction-in-magento
Then add all of your products to your google merchant account. It dynamically shows relevant products that they've already viewed (if setup right). You can further segment and change your spend based on what type of customer they are (spend more for people that made it to your cart page for example...or offer them an ad with a coupon.)
Our experience has been excellent...and it says a lot more than just "Hey man come back to our site"