Two aspects:

1. in a really busy tag like #photography, there are more viewers but also more posters, so although there is money to be made, you really have to hit the sweet spot.
2. On the flip side, some tags have so little activity that even a perfect post for the category won't even be seen. I like to post to #personalfinance, and there doesn't seem to be much action there (yet!).

So I think if you have a great post, make sure to include some of the popular ones. If you're more building out content in a new area, expect it to take longer to build a following. I've been trying to do a bit of each.