I gather that more than 10 was confusing for some. For me large jump lists are very useful– especially for programs that do not make it easy to find and open recent files.
One such program is Windows Live Writer – the program I use to write blog posts. It remembers only the three most recent posts. However, I frequently tweak and retweak recent posts until I get it just right. The more prior posts showing up in the Jump List the easier it is to access and edit those posts.
To change the default number of items in the jump List that Windows 7 makes available: