They say Lady Gaga is the most downloaded performer (or anything else for that matter) on youtube - approaching one billion downloads . She is probably also the most mashed. Here is another great example of why both facts are so. Two versions of the same mashup, from The DJs From Mars
http://youtu.be/VaVa78-03OQ - Metallica "Enter Sandman" vs Lady Gaga ft Beyonce "Telephone"
Here is an extended version with less video work.
http://youtu.be/bjzF0Zf8oSU - Metallica "Enter Sandman" vs Lady Gaga ft Beyonce "Telephone"