Any idea how new of a macbook you would need to power this? I'm guessing my 2012 13" air can't run it right?
"Note that 4K DisplayPort operation is only compatible with the new Mac Pro (Late 2013). 4K HDMI operation is compatible with MacBook Pro (Late 2013) and the new Mac Pro (Late 2013). HDMI input is not available in the European-market Sharp PN-K321."
http://support.apple.com/kb/HT6008?viewlocale=en_US&locale=e...
I did not notice the lag on text input that you did (but, I did not enter much text; I didn't think of this as a possible issue). I also did not notice any significant lag with the mouse. This may be user-dependent.
The thing I did notice is poor rendering of some fonts. There were colored fringes around the system font that both the Apple rep and I noticed. Other common fonts were affected as well, but not all of them. It seemed like a problem with subpixel rendering to me. Changing the display mode to mirroring did not help.
The Mac Pro did not have these problems. It's quite smooth (60Hz) from the Mac Pro.
It was bad enough that it disqualified the monitor for me. I assume it's an artifact of the HDMI driver they're using, and "probably" fixable with a better driver. But you never know.
FWIW, this isn't 30 hz vs 60 hz. My windows box is limited to the same 30 hz and has no issues.
If you want to use a Mac with a 4K display, consider getting a Mac Pro, which can power up to three of them.
While the integrated graphics on the 2013 models can drive 4k displays at 60fps, only Thunderbolt 2 has the necessary bandwidth. The latest rMBPs have Thunderbolt 2, so they should be fine once OS X's drivers are updated. Everything else is stuck at 30fps.
I've used a late-2013 rMBP with a 4K monitor (OS 10.9.1) at 30Hz. It's a supported configuration (http://support.apple.com/kb/HT6008?viewlocale=en_US&locale=e...).