As I have written numerous times before: "finding" (ie search and filtering) becomes exponentially more difficult as inventory grows. Apple's app gallery faces this problem (as do giants like eBay, Amazon, etc). For instance, it is already challenge to discover great iPad apps.... which has far fewer apps available than the iPhone.
Short of implementing Facebook Connect within iTunes and the app store (which would be the ideal solution) - Apple has started to really push the "App Store" page on Facebook. It is a partial solution at merchandising via Facebook and the fans... and, more importantly, it is a way to see which apps are being shared by your friends. Of course, this assumes two large things: 1) that Apple's merchandising on the page is sufficient; and 2) that users actively share their favorites.
While it is far from ideal, they are certainly pushing the effort (see the direct email campaign below) and hopefully thinking about a deeper integration.
Sharing via the Facebook App Store Page
Apple's Direct Email: Join the App Store Page on Facebook
The App Store Page