If you’re experiencing a delay when connecting to an IPv4-only network (LAN or WLAN), you can inspect whether your distro is setting IPv6 configuration to “Automatic” on the first connexion attempt (this is true e. g. for Fedora 16 and openSUSE 12.1). If so, and if your DHCP server (e. g. the router) does not offer IPv6 addresses, Network Manager will wait for an IPv6 address after receiving an IPv4 address until a timeout is reached.

To avoid this lag, you can go to Network Settings, choose your interface (LAN/WLAN/…), click Configure, choose the IPv6 Settings tab and change Method from Automatic to Ignore.