It seems a little wasteful going to the network continuously to query whois to determine something that changes relatively infrequently. I would recommend using one of the modules that you have been recommended to do an initial query of whois and store that somewhere you can query locally. The really smart money would be on using one of the iCal modules to generate alarms in your favourite calendar program or those of your clients at an appropriate time before the expiry. Less is more.

/J\