The users should be allowed to view questions filtered by multiple tags. e.g. I want to see those questions which have tags "ruby-on-rails" and "cucumber" and "testing". It would be much better if we could be able to have an "or" modifier also just like "and".
As you click tags in the "related tags" area they'll be appended to the URL as above.
Just do a search for both tag names in brackets:
Another option is to click on the c# tag and then on the sql-server tag in the list of related tags on the right.