You can search for tags on YouTube, but you cant search for multiple combinations of tags.
The tagging system is abused by inserting lots of non relevant but popular tags.
This filter pipe is an example how YP can be used to overcome both problems: it uses a regexp to filter out videos whose comment is over 50 words long (rare, unless it is a list of spam tags) and it is easy to add more filters. Here up to 9 combinations of tags can be enterted (default is "lamborhini countach" and "ferrari testarossa") But I hope it is clear how you can add as many as you need, just be chaining Union-operators.
Pipe Web Address: http://pipes.yahoo.com/pipes/pipe.info?_id=bJgrLvH_2xGk3qJvE5PZnA