For another great example of this, look at Airport Utility 5 vs 6.
You gain:
* A big shiny globe and background
* iOS-style badges for firmware upgrades
You lose: * Client lists
* Logging and statistics
* IPv6 settings
* Wireless multicast rate, txpower, 40MHz channels, interference robustness
* Printer support
* I'm sure some other stuff
I learned this the hard way the other day. I went to look up a DHCP client and found the table no longer exists! The recommended solution is to install Airport utility 5 ALONGSIDE Airport utility 6. What?! I completely understand the Apple mantra of simple usability, but the power user functions have always been hidden behind that veneer. Now they're just GONE.