Princeton University IT, which keeps a close eye on their infrastructure, claims the iPad is not being a good network citizen:
The malfunction we see is that the iPad uses DHCP to obtain a lease, renews the lease zero or more times (as expected), but then continues using the IP address without renewing the lease further. The iPad allows the DHCP lease to expire, but it continues using the IP address after allowing the lease to expire. The incident continues for some time (typically hours); usually it ends when the iPad asks for a new DHCP lease, or the iPad disconnects from the network.
Princeton says they're communicating with Apple to resolve the issue, but in the meantime they -- and other large institutions -- are keeping the misbehaving iPads off their network.
This won't be an issue for a home user or anyone on a small network where IP conflicts are unlikely, but it's something Apple will need to fix in the near future, especially for the education market for which the iPad is so well suited.
Have you noticed any iPad problems on your network? Let us know in the comments!