Haven't been on the peak in years but it used to be my specialty, so weigh any more recent comments against what follows.
1) If you are a more racing fan that photo nerd, race day is enough (race week is hell on the body), Devil's playground is the best spot to watch from, depending on where you set up shop, you can see about 1/4 of the total course. Be prepared for the altitude and bring lots of layers. I've been there when it hasn't gotten above 40 and they stopped the race half way due to snow/hail, or when there was lightning BELOW us on the course, and when its been 80 degrees. If the weather turns to crap there is a chance they will stop the cars at Glen Cove BUT if it holds out, its the best place. Plan to hit the gate at 4:00 AM or earlier at a minimum and not be off the mountain until after 6 PM. Tons of water, take asprin, and be prepared for 3 meals and you'll have an amazing time.
If you don't want to risk getting stuck and not seeing the action, the ski area or glen cove would be my recommendations.
2) If you are a die hard racing fan or a photo nerd, race day is almost a waste compared to practice and qualifying days. They split the course up in to three sections and the field into three groups. Each group gets one day on each section. Each entrant will get between 3 and 5 runs. They start between 5:30 AM and 6:00 AM and end by 9:30 AM (schedule might have changed a little). You'll need to be through the starting line for the section you want to be on by 5:00 AM to be safe. You can normally park up in areas they don't let spectators park in (safety equipment and broken down racer pull over storage) and or should be able to get up past Devil's Playground on the top. Pick the group that has your favorite entrants in it and follow it, or pick your favorite section and see each group go through it. My favorite spots used to be Boulder Park, up past Bottomless Pit and Devil's Playground (http://www.kevinhahnphotography.com/2009/PPIHC2009D2/) or on the lower section the area known as Blue Sky (http://kevinhahnphotography.com …1KevinHahnPPIHCP3%203.jpg) the Ws or double cut can also offer some amazing views and great photo options: http://kevinhahnphotography.com/2010/PPIHC2010d1/index.html
Practice and qualifying days used to be included in your ticket but they might not be any more (I think I heard that) but in the past it used to be $10.00 a day just for those days. My personal opinion is that race day is great to experience once, but its such a crap shoot, you get to see more action and have MUCH better light on the practice days, you just have to hate sleep and get up at 2 or 3 AM each day. I haven't been back since its been all paved (and some political issues with the organization), but the last year I went, I didn't even go on race day, I did no media credential and just paid the $10.00 to get in on the practice days I wanted to go to, back then there was no waiver or disclaimer on practice days either, just $10.00 ea at the toll gate and that was it, and it was glorious!