Comment 8 for bug 579804

@Adam,
What about making it configurable? Give the user the following options:
- always store tags in original files (and possibly with a sub-option that says "in RAW files too")
- never store tags in original files
- only store tags in files on export

@coffeemonk,
The bug is under review and will be addressed. However, it needs to take into consideration users who may have different requirements. Also, one aspect which is essential, as Adam pointed out, is to not accidentally bork RAW files in doing this, considering that writing metadata to some RAW file formats is considered risky. I'm sure you would be a lot more annoyed if you lost your RAW files than if they didn't contain metadata.
Note that whichever solution is used, this does not prevent you organising and searching your photos by keyword.