Jump is one of my favourite all time songs, so I was worried this was going to butcher it, but luckily it was just the vocals and it turned out alright. Thank god we have Rock Band / Guitar Hero stems to make this kind of mashup really easy now (not sure where they got the Imagine backing track, or whether they just mixed the channels).
As long as you've got two songs in the same key (or can shift it closely enough), similar tempo, and with chord progressions that sorta work together, these mashups can turn out really well like this.