Generally, anything that you add to your page will increase the page weight. This means the file(s) that your server has to deliver to the user has gotten bigger. The higher page weight the longer the page takes to load.
The good news is that Munckin loads asynchronously. What this means is the page does not wait for Munchkin to load. So even if Munckin is slow, the rest of the page will still load.
For example, when you browse the internet, you will probably notice that ads often load after the rest of the page loads. This is because the ads are loaded asynchronously. If you visit TechCrunch, you will notice the ads on the right load after the content loads on the page:
http://techcrunch.com/