I know that Twitter already allow mobile notifications for new tweets from a specific user, but how can I go further and only get SMS (or email) notifications for new tweets from a specific that also match certain words? I know IFTTT doesn't do this, but are there any other ways I can use to do this?
IFTTT just announced new triggers for the Twitter channel, including "New tweet by a specific user" and "New tweet from search". The latter seems like it would do what you want.
The ingredients for the trigger are:
Using Twitter Advanced Search Operators you can get what you need.
As an example, here's a recipe that sends email when Wil Wheaton uses the hashtag "#butts".