On my 4-month old mid-2012 MacBook Pro I observe that Spotlight seems to want to ALWAYS re-index. I frequently notice that the performance will get unbearably slow and I can hear the hard drive clicking away. Then I go and click the Spotlight icon and sure enough, "Please stand by while we index your hard drive." A few minutes later, it finishes and things return to normal.
Please be aware, I'm NOT talking about the first indexing that can take several hours (or all night). "Just let it finish" is not the answer. This is an issue that has plagued my computer for months. The re-indexing jobs pop up every few minutes and finish a few minutes later.
I found an article where somebody is apparently having the same issue, and tried his suggestions to no avail.
I'm at my wit's end! Spotlight is constantly saturating my I/O with its indexing and making my shiny new Mac unbearably slow.
I am grateful for any additional ideas, including more open-ended suggestions about how to go about trouble-shooting such problems in general. Perhaps a command/tool or particular log files which could help me pin down the root cause.