MDWORKER/SPOTLIGHT constant indexing

Ever since my upgrade to Snow Leopard, my CPU has been in constant overdrive mode for days now.
Spotlight is telling me that it is indexing my hard drive, but even after several days it is still saying "Estimating indexing time".

Here's what console says:
+08/09/2009 16:31:37 mdworker[1370] (Normal) Import: Spotlight giving up on importing file /Users/Matt/Library/Mail/Mailboxes/ Stored Emails/Received.mbox/Messages/35901.emlx after 294.11 seconds, 294.109 seconds of which was spent in the Spotlight importer plugin.+
+08/09/2009 16:31:37 com.apple.launchd[1] (0x1006054b0.mach_init.mdworker[1370]) Exited with exit code: 75+
+08/09/2009 16:36:47 mdworker[1385] (Normal) Import: Spotlight giving up on importing file /Users/Matt/Library/Mail/Mailboxes/ Stored Emails/Received.mbox/Messages/35903.emlx after 286.953 seconds, 286.952 seconds of which was spent in the Spotlight importer plugin.+
+08/09/2009 16:36:47 com.apple.launchd[1] (0x1006054b0.mach_init.mdworker[1385]) Exited with exit code: 75+

Looks as if it is trying to import every single message, but without success.
Any idea why the mbox file is giving Spotlight such a hard time?
(Excluding and including the folder from Spotlight Privacy settings has not fixed the problem.)

Thanks for your help!