If you want to tailgate in a car, you’re a dick, but so be it. You’re putting the person in front of you at as much risk as you are yourself. However, on a bike, if you crash into the back of a car that’s stopped and you’re going 60mph (or 30-40mph if you were slowing), you’re going to dent the car and kill yourself. Not so good.
I would actually advocate an even bigger following distance than Rab said, and here’s why: it doesn’t matter if YOU have the skills to stop that quickly, because the person BEHIND you has to notice that you’re stopping and come to a full stop in the same time. While it’s frustrating to constantly have people merging into your lane in front of you because of the space you’re leaving, having more space (3-4 seconds all the time) allows you to SLOWLY come to a stop, ensuring the person behind you doesn’t make motorcycle man sandwich meat out of you.
Two more things. First, what CB and Rab said about earplugs is a definite must. Wind noise is super loud on the freeway, and it will not only fatigue you mentally, but it will as they say contribute to hearing loss and other undesirable things. For your riding, however, the biggest benefit of earplugs is for your concentration. At higher speeds, earplugs will kill the wind noise but leave you plenty of hearing for your engine, making it easier to know what your bike’s doing and distracting you less.
Second, like everybody has said, once you get accustomed to the speed, the freeway’s not so bad. It eliminates intersections (which are the devil for us two-wheelers) and oncoming traffic (for the most part). However, you have to grow even more sensitive to the position of cars around you and to people being idiots and trying to merge into your space (which WILL happen multiple times per ride…drivers are blind; fact of life). Therefore it makes sense to desensitize yourself to speed first, then worry about getting comfortable for long stints. What I did was actually just get on and off the freeway for a few exits one day. The very first time you open the taps on your motorcycle, even if it’s a 250, you will be a bit taken a back. The sense of speed is much greater without the car all around you. Just get on the freeway, ride a couple miles, get off, and go back home. You’ll get used to the speed very quickly.
Do the obvious, however, and stick to your guns. If you feel uncomfortable, scale it down and take it slow.