I've been considering sending a plaque with a CD and inscribed with their first dance at the one year mark but just haven't yet. At present, I follow up with a few emails about 2 weeks after the fact and ask for weddingwire review. I will ask them to be facebook friends but no way am I going to just put them on an email list, once their event is past. The majority of the cases, seems they create a temp email account for wedding planning anyway.
I have been debating on whether it's best to go after online reviews or send them a piece of paper and a return envelope. I wonder if it wouldn't look more legit to have scanned copies of the (nice) comments on the website. I've been asked before if I faked WW reviews (I don't).