We used it all to great success ... along with our Linux hosts. We had a stack of T1's and eventually a few thumpers (x4500's) which we ended up running a variant of OpenSolaris on. There was also some bigger iron that was humming along on Solaris 8 which provided a very stable environment (until I fat-fingered a command one day.)

Later on, we even ran an ipfilter based router from a T1 on OpenSolaris for decent IPv6 connectivity with link-aggregation+vlans when our Cisco 6509 setup was found to be inadequate for the task.