I've been waiting for Muddy Cup to post a reply, but I'll weigh in with my 2 cents...
Our shop is like dant's in that we offer 2 sizes, 12oz. and 16oz.. We have had a number of requests from our customers to offer an even larger size, and we are going to do so; we're going to add a 20oz. in the next couple of weeks.
While I agree with the principle of "its my shop and I'll have what I want", sometimes you need to decide which battles really matter to you and which ones don't. Ultimately, we are in business to make a profit so that we don't have to work for someone else. To that end, if you have customers that are asking for something, it would pay to at least look into carrying it. If it is easy/inexpensive for me to get, I figure why not, and just do it. Other things are more expensive, or just aren't what you wanted for the overall feel of your shop, so that's something that you would want to take a closer look at and be sure to justify going forward with it.
As an example, we've had a few people request that we have "normal" height tables instead of the furniture that we do have. While I appreciate them taking the time to provide us this feedback, adding these furnishings is not in keeping with our overall ambiance and style. This is a battle that we are choosing to fight and to use the "its my shop" mentality. Other things, such as adding wireless Internet access, we are currently evaluating because we have had a number of people ask us if we offered this, and its starting to become something that we may add because it will be an added draw, and hopefully translate into overall better sales.
There, I think I'm done with my lecture. Sorry for the length, but I wanted to be sure that my point got across fairly clearly. Feel free to provide your thoughts on the above, I'm always willing to see a different point of view.