Now comes the question if you think mash-ups are legitimate displays of musical talent?
Personally I think the ability to make two or more songs become one is a great skill. You have to both have the ear to know what would sound good together aesthetically, but also the lyrics have to match up, the beats, the vocals. Plus, a great understanding of computers programs in order to make the songs work the way you want them to. I think mash-ups are just as legitimate a music genre as pop or hip-hop, etc.
Here is the catchy compilation of the top 25 songs of 2009!