Jeff,
Between 2 businesses, we ship over 1000 packages a year USPS. The service is really pretty good, and if you are shipping to mainly residental addresses, by far the least costly. Also, if you use Priority Mail the shipping containers are furnished at no cost to you. With that said, I would recommend looking at USPS.com. I would use delivery confirmation on every shipment. If you print your own shipping label there is no cost for this on Priority Mail, and it is discounted on 1st class and this gives you a way to track the shipment. Are there problems with shipping USPS? Sure, but I could tell you some real horror stories about UPS and FedX as well.
Ben