Is tai chi an effective stress reliever?

Yes: Yes, if you enjoy tai chi it can be an effective stress reliever. It combines gentle movement with a meditative approach, training mind and body in a healthy way. You need to have a good teacher though, who embodies the principles. There are videos, but probably this isn't as good as having someone you can ask questions of while you're practicing.

Yes: I agree with dr. Pappas. When i took tai chi in japan, i was at the point in my life where i wanted something that was faster and more physical - so tai chi actually frustrated me. If you are able to move slowly and breath mindfully - than it will likely be very beneficial in calming & grounding you.