Having useful tags on deals helps them to show up easily when someone does a search, but from what I've seen the majority of deals don't get any tags.
to encourage tagging I suggest having an emblem for it, so that people will use the function more. Maybe have it with different levels like leaving comments.
There will be some people that will leave rubbish tags, but that could happen now, and as for people spamming it just for an emblem, the same could happen now with getting post count emblems.
I just think that this feature is not really being used enough by the community, and that this would be one possible way of promoting it and make it work better for finding deals.
What do you think?