Since the multi-tag search off Last.fm Playground is not working or otherwise, shut down, I found a solution to multi-tag searching in a DIY fashion. It's ridiculously easy.
Here's a few things you will need to do.
Use Google.
1.Go to http://www.google.com/
2. Do the following by copypasting this into the google search: www.last.fm/music intitle:"tags for" "insert tag" secondary tag
Example: www.last.fm/music intitle:"tags for" "post-rock" shoegaze
3. Happy multi-tag searching!