Both YadaYada and Omnisky use the Novatel Minstrel "S" Wireless Springboard Modem (whew! Say that three times fast!) which is a "true" SpringBoard in that it installs software on insertion, and uninstalls (some) software when removed. This makes installation truly plug and play. Both services install their software the first time you insert the springboards. YadaYada's install is very transparent, while OmniSky's has a progress bar that explains what is happening. OmniSky's install requires a soft reset, while YadaYada's didn't. YadaYada replaces your App Launcher with their own.
Both services launch their "Home" pages when your press the hardware button on the modem. YadaYada takes to you their launcher, OmniSky takes you to an offline OmniSky home page.
If you yank the modems while either service is using it, all bets are off. The theory is that the system is suppose to gracefully handle it, but I've had some HORRIBLE things happen. This appears to be a problem with the Minstrel, and not the Service, but it certainly reflects poorly on everyone involved. I've hard reset 3 times, including a lovely crashing infinite-loop reset. I would suggest that if you are going to take the leap into a Wireless Springboard service that you also take the leap into a $40 Springboard Backup Module. Trust me. I hope that Novatel choose to release a firmware update to fix these problems. Until the, make sure that you go into the included Minstrel Modem application and turn the modem off before you yank it.
YadaYada's Installation is seamless and quiet, but OmniSky's offers a information and status during install. I'd say it's a tie for Installation.