I would venture to say that 95% of the apps I have currently installed on my iPad 3 have been updated to use a higher resolution. One of the holdouts had been Temple Run but they recently updated it for the new iPad. Even then, apps that are made for the iPad 2's resolution still don't look any worse than they do on the iPad 2. The ability to view higher resolution photos trumps any apps that are still lagging behind and haven't been updated for the higher resolution display.
64GB iPhone 5 | 64GB iPad mini | AppleTV 2 (2012) | AppleTV 2 (2010) | 2012 15" MacBook Pro, 1TB SSHD, 16GB DDR3 1600 MHz, OS X 10.8.3 Mountain Lion | Apple Lossless | iTunes AAC 192kbps VBR | iTunes 11.0.2| Library size = 1.04TB | Legacy iPods: 3G 40GB, 4G 40GB, 5G 60GB, 160GB iPod classic (2009)