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Lightroom 2 - Keyword Tags
Since upgrading to Lightroom 2 from Lightroom 1.4 I have noticed an issue with Keywords not being exported as part of the EXIF data. The problem, so I found out is that the keywords have the Include On Export keyword tag option disabled.
After a little bit of research I found a few options to resolve the issue. What I ended up doing was downloading installing and running the AdjustKeywordOptions.lua script from Adobe. I haven't had the problem since.
Rather than repeat everything here is an article from the Adobe Knowledge Base.