There are a number of missing features on the Time Capsule (any Airport) which is why I still use a Linksys WRTG54GL with Tomato firmware as my router, with the TC in bridge mode being used strictly as a wireless AP and GigE switch.

The two main things I was looking for that TC didn't provide were manual QoS settings, which I use to prioritize VOIP traffic, and a bandwidth monitor. This last one should be possible using SNMP which the TC does support, however I was never able to find a usable SNMP client - the simple bandwidth logging ones just didn't work.