There's some confusing and misinformation on this thread. I hope I can clarify some things.

Saddle Road doesn't take you to the
observatories, it takes you to the roads to the observatories. It's really not a big deal. Rental car companies don't want you there because there are no services and it's an expensive tow if your car breaks down. (They do allow the scientists working at the observatories to take their vehicles on Saddle Road and up to the observatories.) Cars also use more gas at higher elevations, so make sure your tank's full. It is paved, but not well maintained. The edges of the road are rough, meaning if you can drive in the center your ride will be much smoother. We didn't really find the road that bad. There were no major potholes that I can remember. It was just uncomfortable if you had to ride on the edges, which appeared to be deliberately designed to give you a washboard feel - guess that slows people down. It can also be foggy in parts and it's not lighted. (Obviously, don't drive in the center if there's fog.) Personally, I think you can be safer on it at night simply because you can usually see headlights from a good distance.
ASAIK, there is still one independent company - Harpers? - that allows you to take their vehicles on Saddle Road, but when I checked they were quite expensive. We've taken our regular 4WD rental and it was no problem. We did hit a bad patch of fog, so do use caution.

John A. Burns Way comes off Saddle Road about marker 28 and goes up to the visitor center where they have Star Parties most nights. Basically, a bunch of astronomers are there with portable telescopes set up and aimed at whatever happens to be out. Burns Way is paved to the visitor center. Do a search on the Mauna Kea visitor center to find out the star party hours/days. The road to the visitor center is steep, but not so bad that you can't do it in a 2WD. I've seen lots of 2WDs up there. Beyond that, the road is not-paved for four miles or so and then it's paved again. They do keep you from going up at that point if you don't have a 4WD. Visitors also aren't allowed at the top after dark. If you do get a 4WD, you can go on a daytime follow-the-leader tour up to the major observatories. You follow them in your 4WD.

While the summit has all the observatories, these aren't the kind of telescopes you look through and only one - Keck - lets visitors in to the gallery see its scope.

I don't know when you're going, but they do get snow and, as I mentioned previously, it's freezing cold up there (even at the star parties) so dress warm. The visitor center does have hot chocolate, tea and coffee.

It really comes down to a couple of things:

1)If you're going to rent a 2WD your only real option is going to the visitor center. I can't think of any reason to go there during the day.

2) If you rent a 4WD (and most rental companies don't guarantee a 4WD, just a SUV which could be 2WD), then you have the option of going up during the day and seeing the summit. I suppose you could time it so you came down and hung around the visitor center until the stars came out.

Before we'd ever done this trip, we'd read the horror stories too. Once we did the trip, we pretty much thought it was a piece of cake and wondered what all the fuss was about. That's not to say there's never been an accident on Saddle, but as conjested as Hawaii has become, you're probably as likely to get in an accident most anywhere else on the island as on Saddle Road.

[This message has been edited by letiole (edited 10-17-2003).]