The first time I went to Bahn Thai (December 2007), I wasn't pleased at all. The dining room isn't anything special, the service was apathetic, and my mock duck curry wasn't impressive.
I have gone back twice recently. Our waitress was helpful and funny. My food was so much better than a year ago that it was unbelievable. When you order 4-stars (as spicy as they'll go), you get pretty little peppers in your meal that are as tasty as they are hot.
What it comes down to, for me, is that if a place is (happily) open to substitutions AND can make a dish spicy enough to please my high tolerance, I can't help but be impressed.