If you want to know how reliable UDP is, ask a VoIP engineer. The audio component of VoIP calls is called RTP (also referred to as media). Media is passed using UDP, because there's no point in retransmitting voice packets. The time sensitivity of voice communication makes it a frivolous act. By the time the retransmitted packets arrive, the audio stream has already been reassembled and played back to the end user with defects.
I used to run a pretty sizable VoIP network over a DS0-based Carrier Ethernet network. When you have tight control over the network, UDP is extremely reliable. We would go long periods of time with 0% packet loss (as reported by AdTran VQM). When we did see loss, it was normally because of a problem we were already aware of. That's the beauty of DS0. When a DS0-based circuit drops frames, alarm bells sound.
I used to run a pretty sizable VoIP network over a DS0-based Carrier Ethernet network. When you have tight control over the network, UDP is extremely reliable. We would go long periods of time with 0% packet loss (as reported by AdTran VQM). When we did see loss, it was normally because of a problem we were already aware of. That's the beauty of DS0. When a DS0-based circuit drops frames, alarm bells sound.