There definitely seems to be a memory leak. When first started, it used just under 100mb, but at the moment it is using almost 600.
The usage starts to climb as soon as you start browsing the iTunes store, so my theory is that it's similar to the memory leaks Safari used to have where it would not release ram after doing lots of browsing. After all, when browsing the itunes store, it's simply acting as a web browser. It's probably keeping all past pages in ram and not releasing it ever.