In this work we study the effect of TCP feedback traffic in IEEE 802.11b--based WLANs. In particular, we present an analytical model which allows to evaluate the impact of the delayed acknowledgments option on TCP throughput. Furthermore, we investigate the impact of such mechanism on the session delay for short TCP transfers. We show that, by carefully tuning some system parameters, both bulk TCP throughput and session delay may benefit from the use of delayed ACKs.