I'm having the same problem you are, and I'm exploring options.
First I noticed that Backblaze (backup service) was causing the problem, but I fixed that by including the /library/backblaze folder in Spotlight's privacy area. The complete lockup that was causing is now no longer a problem.
However, I'm noticing that most of the cycles are going to indexing my Time Machine backups, which Spotlight will not allow in the privacy area. It looks like it's indexing many of my old mailbox files from mail.app that are backed up on the Time Machine (Time Capsule) disk. I really don't see the logic to this. I've had the computer on and idling with full access to Time Machine for many days now and this is still going on, with MacBook Pro fans running at full gun and CPU not quite maxing out, but frolicking between 5% and 65% or so on a regular basis with no other apps present. Activity monitor doesn't show anything else hogging cycles -- it's all mds and mdworker.
Something isn't right with this. I hope that the next update from Apple will fix this, or someone on the intertubes will come up with a quick solution.
All the above is on a MacBook Pro (late 2008). I do note that I have a MacBook Air (late 2010) that backs up to the same Time Machine but does NOT have Backblaze installed. (I put everything important on the MacBook Pro.) This machine does not seem to have these problems. Both computers are running Lion and have much of the same software. Backups are doing fine on both machines.
My temporary solution is to turn OFF Time Machine on the MacBook Pro. This does seem to make things much better -- although even at 5% CPU use the fan runs somewhat higher revs than I was used to with Snow Leopard. I then run a manual Time Machine cycle just before I turn in for the night. When I'm back to using the machine again, I make sure the Time Capsule is not mounted. I'm backing up any working files continually to Backblaze still, as well as to Dropbox, so cutting the Time Machine frequency down to once or twice a day is not too bad for now. I do not want this to continue, however.
Also, I have done the following: Repaired disk permissions, reset the SMC and PRAM, and started the computer up in safe mode fully, and then restarted in regular mode.
If anyone has any possible fixes, I'm listening and thanks!