I made my largest (4 tier) wedding cake last weekend. I've only done a couple of "real" wedding cakes. Anyway, I thought the cake turned out fine but am slightly disappointed that the bride & groom have not bothered to email me to say what they thought of it. I'm sure they would have contacted me if there was something wrong. To be honest, I'm only disappointed as I was hoping to put their feedback on my website as I only have one relating to a wedding cake. I wonder if you guys email all your customers after delivering cakes to get their feedback or just leave it. Also, I don't really know what to say in my email either.
They just got married! I think they have other things on their minds besides the cake! 
You might just wait a while and if you're still curious email them with a customer service approach, thanking them for the opportunity to be part of their special day and the hope that you are considered for all of the special events in their lives. If they write back I'm sure they will have lovely things to say. If they don't I wouldn't pursue it.
The problem with contacting clients after the fact is you are leaving yourself open to 'the cake was great, BUT Aunt Sue said it was dry...can we have a refund?"
Be careful what you wish for! 
Umm ... yeah - I'm thinking they might be kind of, you know, busy right now. I'd say give them a little more time. At least a couple more weeks. Then, if you haven't heard anything and you're still wanting the feedback, send the business-type email as mentioned above.
Sometimes I don't hear back from brides at all. Most of the time, actually. You definitely don't want to hear from them the day after the wedding, because that's usually a complaint!
No news is good news in this business.... at least that is what I tell myself.
Majority of people don't call or write unless there is something wrong. Think about it.
They're not going on honeymoon for another few weeks yet and besides they live together anyway. How can they be "busy" - he he he!!!!!!!!!!!!!
They're busy cleaning the house or something then!
Seriously, do you call everyone who you buy things from and thank them? I don't, so don't worry about it. If you want the feedback email in a week or so like other people have suggested and ask how everything went. I know it's hard waiting if you expected to hear from them, but most people don't send feedback.
When I buy stuff off Ebay sometimes the seller will send me a message something like "Thanks for your recent purchase. I work hard to receive good ratings - please take a few minutes to leave feedback. Thank you again for your business..." If you really want the feedback, you could try something like that. Of course, there's always the risk of receiving criticism as well as praise. I would still give them more time though. The only people I hear back from in a week's or less of time is family.
I mail a hand written thank you note to all my brides. Something like this:
Name of Bride and Groom,
Thank you for choosing ________ to provide your wedding cake. It was a pleasure working with you both.
P.S. (something personal: center pieces were beautiful, hope they got the power outage fixed in time for the reception...)
Since I started doing this, almost all of the brides have either emailed me or sent their own thank you card back. I then email them that if they post their review (since I know it will be a positive review) at one of the following sites (I list 3 sites I am on that allow reviews) I will send them a coupon good for 10% off their next purchase.
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