I now leave feedback as soon as payment is cleared. The buyer, after all, has completed their part of the deal.
I also let them know :
1. That payment is cleared
2. I am posting today (or tomorrow if they've missed today's mailout)
3. I have left feedback, and please leae feedback for me when they receive item, or contact me if a problem.
I am big on communication. I acknowledge every step and my customer appreciate it.
Being upfront and honest with buyers has never caused me any problems, the opposite in fact. I have many repeat customers because they know they will get they pay for, with great customer service. Yes, it takes a little more time, however it's worth it. :-)