a couple of drives might go bad after spinning down and then they refuse to spin back up. Label everything as you don't want to mix up DAEs/buses :). Lastly ..backup backup backup

In addition to what Dynamox said may I suggest backing all the data on the array a few additional times.   Seriously though, just to be safe:

1) Make damn sure you back up all the data twice.

2) Label every cable one each end with both end data sets.  Labels come off.  Been there... done that.

3) Be aware you will loose disks.  The rubber mallet method won't work well any more.

4) Make sure you soft zone your array.  If you accidentally connect up a fiber cable wrong, it won't kill you.

5) Be damn sure your racking team does NOT power on any part of the array until all the devices are moved, and plug it in top down.  SPEs then DAEs.

For the power down, I would advise following the Clariion Power Down Procedure (there is a doc for the power up/down procedures on Powerlink somwehere):

1. Clear all I/O (I usually shut all servers and power down my switches)
2. Disable write cache and wait till assigned cache pages is 0.
3. Power down the array.

Hope that helps.