tmatk
Explorer
You all really need to re-evaluate the technical competence of your web staff if you need to be down for a week or two to perform an upgrade. I design the backend of enterprise web applications for a living, and if I proposed 1-2 weeks of downtime everytime our software was upgraded, I'd be out of a job in a flash. At the least, is there not a staging environment to which your new website software can be installed and tested against while you leave your current website up and running? This is standard practice in the industry.
I have to agree. Shutting down your entire site for that long is just... bizarre. I don't care who you are or what upgrades you are planning, you will lose many viewers.