As per the summary, users should be able to add free-form tags to each transactions, and then use the tags for searching, filtering, and in reports.

Someone may say that account tree is already categorizing transactions. That's right. But it's important that one transaction can have multiple tags. If I can tag my checkbook, I can easily figure out how much I have expended for my trip to Thailand. I can also track how much I have spent money for satisfying my girlfriend. And I may want to track bad choices, money I wasted, shouldn't have spent. Just tagging comma separated tags like THAI2010, 9THGF or WASTE to each transactions and tag searching will do this. I think tagging is easy and general solution for these purposes and others--YES, this can satisfy users requesting more fields to the transactions like owner, location, and whatever so on.