When I upgraded to Mavericks last night my computer was like it was running through molasses. Long story short I figured the biggest part of the slowdown was Spotlight trying to index my Terabytes of data. Here is a document I created a while back that I used to get control back and I’m posting it here in case it helps anyone else.
In my case I ran it to stop Spotlight, unmounted all the backup drives, and I’m bringing one set of backup drives back online as Spotlight gets each previous drive sorted. I’m leaving one set offline so I don’t overwrite my last good copy of Mountain Lion before I mean to.