Getting as much of the system hot-swappable is vital if you want to maximise your uptime.

I have a Dell PowerEdge 2600 (Single XEON 2.4G (will upgrade to dual if required),RAID5,2G RAM,Hot Swap Drives,Fans etc.) and have just heard that there is a recall on the fans. Because the system has hot-swappable fans, the tech will simply swap them one by one without having to stop the system. As the techs will only come out during business hours this is especially critical.

A redundant power supply is good too. It means that you can move your server without having to power down.

Cheers,
Jamie