I am noticing the same issue, immediately following the upgrade to 10.7.5 (combo download). I see the same behavior on two entirely different pieces of Apple hardware, a 5+ year old MacBook Pro, and a mid-2011 MacMini.
On both, I disabled Spotlight prior to the upgrade, to provide the easiest path to getting the system running on the new release. Prior to 10.7.5, Spotlight, running from building a new index, has never taken longer than 30 minutes on either machine (I have <20GB data on boot drives).
When I re-enable Spotlight on the upgraded machines, it takes as long as 30 minutes just to get an "estimate" of indexing time. The estimate varies during the indexing period, from days to hours. On the Mini, it has been running now for 24 hours and the blue progress bar is almost done. It has been estimating 5 or fewer hours left for the past 12 hours.
One thing I have noticed via Activity monitor, if you sort the display on "%CPU", so the most active process comes to the top of the list. Prior to 10.7.5, you could see mdworker processes right up at the top during the 30 minutes it took to index. This always made sense, because they were churning out an index, and it got done rather quickly.
Since 10.7.5, except for very brief spurts of activity, the mdworker processes are using almost zero CPU. This would jive with the resulting slow indexing. If mdworker is not working, then it is not producing results 😠