Just remember, our posted speeds are in miles per hour, eh.
July 4th weekend? Don't try to drive anywhere late Sunday night. That's when the drunks will remember they have to work the next day and try to drive home. Other than that, don't try to drive on the SoCal Freeways during rush hour (roughly 7am-10am, 4pm-7pm Monday-Friday). Same goes for most urban areas.
How long it will take depends on how many hours you can safely drive in a day. I once did a road trip where we went non-stop (except for gas) from SoCal into BC in about 24 hours. Took turns sleeping and driving, had a cooler full of sandwiches and soda. If you're not that crazy, maybe Mt. Shasta on day 1, Anaheim on day 2. That's about 12 hours a day of driving. Figure a 4-5 days going back if you're really going up the coast (Hwy 1 and 101) on the way back and stop to smell the roses. And make sure to see Hearst Castle if you go that way.
From Anaheim to San Simeon will take you 5-7 hours if you take Hwy 101 to San Luis Obispo depending on traffic. I recommend a stop in San Luis Obispo for dinner, then stay there or San Simeon and take a couple of Hearst Castle tours early in the day, then head up the coast to Carmel/Monterey. Spend the next morning exploring San Francisco, then up to Mendodino/Eureka/somewhere in that area (I really have no idea which of thise towns is nice, just going by time and miles). Then to Portland via the redwoods. Next day, home. That really shortchanges San Francisco in my opinion but that's already 2 days down and 5 days back. 4 days back if you don't stop in Portland but make a 13 hour push for the finish.
The drive north on Hwy 1 from San Simeon will be slow. And that's assuming the road is open all the way through. Sometimes it will be washed out or locals-only for months at a time. Right now it's open to all traffic with a 1-lane section expected to be back to 2 lanes by 7/2/10. It's a beautiful drive if you've got the time.
With 3-4 days at Disney, that pretty much uses up all of your time but I'll throw out a few SoCal suggestions.
There's Six Flags about 1.5 hours north. Good if you like rides, rides, and more rides. Not so much for ambiance, tho they'd made a lot of effort to improve the cleanliness of the park the last time I was there. It was a noticeable improvement over 5 years ago. Admission is relatively cheap (Under $30 with a coupon and steep discounts on next-day returns).
About 1.5 hours to the south are the San Diego Wild Animal Park and San Diego Zoo. They're both good for a full day each. Check their website (I don't have enough posts to include a link) to see if they have any special events or tours going on. Sometimes they'll have interesting behind-the-scenes tours available for an extra fee. Their admission prices are kinda steep at $37 per person per park but you can get an annual membership to both parks. It's $99 for two adults in the same household (parent and 18 year old) and gets you two additional free guest passes (for the 13 year old). Even if you only go to one location one time, you'll still come out ahead.
Of course, there's Sea World to the south and Universal Studios to the north. And I think there's a
LegoLand down here somewhere. There's the Discovery Center in Santa Ana. If you want water parks (it'll be hot in July!), there's Raging Waters in San Dimas and Wild Rivers in Irvine. In addition to Sea World, there's Aquarium of the Pacific in Long Beach. There's the La Brea Tar Pits. Nixon Library in Yorba Linda and Regan Library in Simi Valley. The Queen Mary in Long Beach (but no longer the Spruce Goose).
Lots of stuff to do.