I find users do often ask related questions as comments to answers, follow up questions to detailed answers, mainly. This threatens to clog up the forum, so that's when I point out the Related Question button. For me it works great, and I would never have thought of implementing it myself (kudos!).
I wouldn't be too interested in a related to the question button, though, since it's pretty obvious what to do if you have a similar question, and people don't seem to post such questions as answers or comments.