For a typical large company, you will probably get an association to an Access Point within seconds, and as most companies don't even use WEP or MAC address filtering, you're in. Wheeee!
If WEP is used, you might have to sit around for a while until Airsnort is finished (time varies depending on network traffic) and then you might need to spoof your MAC address if the network admin has a slight clue.
Companies using VPN's for this - few and far between at the moment, so lots of consultancy for me