I'm having this problem since 10.7.5 as well. ~/Library/Spotlight does not exist (only one user account), and /Library/Spotlight contains no importers. So it could be a 3rd party application importer: Colloquy, Evernote, LibreOffice?
Console reports this:
Oct 1 14:51:55 mingisapsycho mdworker[317]: Unable to talk to lsboxd
Oct 1 14:52:09 mingisapsycho mds[66]: (/.Spotlight-V100/Store-V2/92954810-8470-4933-A363-3E87B3D6F841)(Error) IndexStore in bool setLocalizedAttributesLocked(datastore_info*, db_obj**, const __CFString**, const __CFDictionary**, CFIndex, StoreOptions, const __CFDictionary*, bool, bool, const __CFArray*):Error:7 setting field:com_apple_system_prefs_keywords for oid:292103
and
Oct 1 14:53:49 mingisapsycho mds[66]: (Error) ImportServer: <MDSImporterWrangler: 0x7fc6a161b120> still waiting for plug-in info from mdworker
Oct 1 14:54:54 mingisapsycho mds[66]: (Error) ImportServer: <MDSImporterWrangler: 0x7fc6a143a800> still waiting for plug-in info from mdworker
At the same time as the waiting for plug-in, 'sudo opensnoop -n mdworker' reports this:
501 364 mdworker 3 /dev/autofs_nowait
501 364 mdworker 4 /Users/chris/.CFUserTextEncoding
501 364 mdworker 3 /dev/autofs_nowait
501 364 mdworker 4 /Users/chris/.CFUserTextEncoding
501 364 mdworker -1 /Library/Sandbox/Profiles/mdworker.sb
501 364 mdworker -1 /System/Library/Sandbox/Profiles/mdworker.sb
501 364 mdworker 4 /usr/share/sandbox/mdworker.sb
501 364 mdworker 5 /var/folders/9h/nxvdj4k96zsg_6pkghc465lc0000gn/C//sandbox-cache.db
About 10 minutes later in console:
Oct 1 15:04:42 mingisapsycho mdworker[379]: Unable to talk to lsboxd
And at the same time with opensnoop:
501 380 mdworker -1 /Library/Sandbox/Profiles/mdworker.sb
501 380 mdworker -1 /System/Library/Sandbox/Profiles/mdworker.sb
501 380 mdworker 4 /usr/share/sandbox/mdworker.sb
501 380 mdworker 5 /var/folders/9h/nxvdj4k96zsg_6pkghc465lc0000gn/C//sandbox-cache.db
89 379 mdworker 8 /var/folders/zz/zyxvpxvq6csfxvn_n00000b400002s/C//mds/mds.lock
89 379 mdworker 12 /var/folders/zz/zyxvpxvq6csfxvn_n00000b400002s/C//mds/mdsObject.db_
89 379 mdworker 13 /private/var/db/mds/system/mdsObject.db
89 379 mdworker 12 /var/folders/zz/zyxvpxvq6csfxvn_n00000b400002s/C//mds/mdsDirectory.db_
89 379 mdworker 13 /private/var/db/mds/system/mdsDirectory.db
89 379 mdworker 12 /var/folders/zz/zyxvpxvq6csfxvn_n00000b400002s/C//mds/mdsObject.db
89 379 mdworker 12 /System/Library/Security
89 379 mdworker -1 /var/empty/Library/Security
89 379 mdworker 8 /var/folders/zz/zyxvpxvq6csfxvn_n00000b400002s/C//mds/mdsDirectory.db
501 380 mdworker 4 /System/Library/Frameworks/CoreServices.framework/Frameworks/Metadata.framework /Versions/A/Support
501 380 mdworker 4 /System/Library/Frameworks/CoreServices.framework/Frameworks/Metadata.framework /Versions/A/Support/mdworker