The transporter would be the single most useful system to have.
Trying to send a man to the moon? Use the transporter!
Want to visit the other side of the planet during your lunch break? No problem!
Want to steal vast quantities of gold from the national reserve? Success is just a click away!
Hmmm....nevermind, we'd just turn it into a weapon and make the world go boom. too bad, it could've been awesome. Like Shatner.