I have absolute HAD IT with the USPS. For the first two years they were great, but we've had almost a dozen packages that were two weeks late without explanation and no tracking updates and two lost packages (fortunately cables) in just the last month or so. USPS doesn't answer the phone anymore, either. I was on hold for 2.5 hours today before I simply had to hang up. I wanted to use USPS, but it is becoming untenable.
We're going to turn on Fedex this week and we've got good rates. It's not yet clear if the notifications for the system will be more reliable, but I have verified the integration is working to get accurate shipping rates so we're getting closer.
For notifications, we use PayPal for all our payment processing and shipping, but the problem is if you register at www.mrspeakers.com with an email that is not in use at PayPal they won't send a shipping notice. If you use a credit card and an email registered with PayPal they do send a notice. I call that a bug, they say it's a feature, and that it won't be changed. This may not change when we add Fedex, this is something we're working on.