And double, triple, quadruple check the IP to make sure it's your's. Being half asleep last night I tried over and over again to figure out why a new client couldn't log into his ftp account.
Finally I submitted a rather jaded ticket to my datacenter tech staff asking them why one of my IP's was bound to someone elses' server.
This was quickly followed by the realisation that I was an idiot and told the guy 113 instead of 213. Needless to say that after I got my foot out of my mouth I asked the tech guys to cancel the support ticket :P
The moral of the story is make absolutely sure you have the right IP. 1 little # wrong caused me hours of hairpulling and worrying that I might lose a very important corporate customer just because he couldn't ftp into the server.