Unfortunately I feel most musical mashups fall under Lauren's category of not worth the effort of listening to completion. I don't think this means musical mashups as a genre is a failure -- just that's it's hard to do a really good one. Taking two (or more) tracks and make something not just 'okay' but better than each of the originals? That's, well, difficult. Gems can be found. I know someone who considers this mashup of Bittersweet Symphony and Brush that Dirt of your Shoulders one of his favorite songs. The best one I've found so far is Q-unit. Seriously though, this fusion of Queen and G-Unit is good. No, really, try 'Old Fashioned Outta Control Loverboy.'
Movie mashups are fun. I looked around on YouTube and found a bunch of interesting ones including sequels to Titanic, Pirates of the Caribbean and others. It's partly fan-fulfillment but these videos are fascinating to look at regardless. I even found myself thinking I'd watch some of these in theatres. I sat around late at night one night last week with some friends and watched a couple of these along with a bunch of miscellaneous youtube videos. Unlike their musical components, we enjoyed these just as much as their non-mashup components. Sure we loved the liam show's 'love letters' or the occasional snl skit but it appeared the mashups had equal footing.
In contrast, I don't know what a good photoshop is equal to. The idea of a photoshop is so uniquely based on the idea of mashups that I can't think of a non-mashup equivalent. I guess I've seen pages that just post funny pictures but with nowhere near the frequency of places like worth1000, fark, or somethingawful. They really cater to our sense of immediacy because we get tons of them without any particular need to let our attention rest on one. While I was writing this I was going to go off on some tangent about how there isn't really an application outside of these contests for photoshops but I remember this really creepy site I saw on somethingawful a couple of months ago. "Natural Beauties Contest" is site where people pay to have pictures photoshopped for pagents or personal use. Look at some of the retouches if you want to know what I’m talking about. Some of the changes appear to mashup real photos with doll like qualities. Strange to say the least. Maybe this is just a whole new level of airbrushing that is gradually becoming more and more acceptable in society?
I think I meant to talk about the external viability of mashups now that the technology to create them is becoming increasingly widespread. Or maybe compare the originals to mashup but my ideas, like my post just kinda blurred into one rant. I feel like the old man on the porch yelling at kids while trying to figure out why everyone likes these new-fangled gadgets.