Packet detection and timing acquisition for IR-UWB networks such as 802.15.4a relies on the presence of an acquisition sequence (or preamble) at the beginning of each packet. A simple network design choice is to use a common acquisition sequence for the whole network. A second design choice is to use an acquisition sequence private to destinations. It potentially yields a larger network throughput, but requires additional complexity for sources to learn the acquisition sequence of their destination. In this paper, we evaluate the effect of a common or private acquisition sequence on the network throughput. Our analysis is based on analytical modeling and simulations. We show that a private acquisition sequence yields a substantial increase in throughput. The throughput difference grows with the number of concurrent transmitters and interferers. We also show the presence of a compounding effect similar to the exposed terminal issue in 802.11 networks.