First things first, if your car was fine yesterday, and is shaking today, get out and check the tightness of your lugs (the bolts that hold your wheels on). There's nothing like being passed on the highway by one of your own wheels, especially when fate lets another half a block pass before the wheel-less side of your car hits the pavement. It'll take years off your life.
But let's say you have a typical vibration that shows up around 55 or 60 mph. This is definitely not something you need to rush to the shop about. It's certainly not good for your car. All that shaking can cause premature wear on your tires and suspension components, but it's a slow death that you can wait a week to address, if you must.
Perform a few checks, including tire pressure and wheel balancing, to see if it's something that's an easy and cheap fix. If that doesn't help, it's time to visit the repair shop. Their diagnostic machines can tell you in five minutes what it would take you and me a month of replacing things that aren't even broken to get to.