The thing that lead to the accident in LA (the one that hit the apartment building) is the most common cause of VFR accidents. It's officially known as "continued flight into IMC under VFR". Basically, it's when a VFR-only (Visual Flight Rules only) pilot flies into IMC (Instrument Meterologic Conditions). IOW, a pilot who is only certificated to fly by visual references gets into weather where the visual references disappear and you have to fly "by Instruments". To legally fly under IFR (instrument flight rules) requires additional training and additional equipment on the airplane (although my guess is that the Beech probably had all the necessary equipment - just a pilot who didn't know how to use it).

The other contributing factor was what pilots call "get there-itis". Apparently this guy was trying to get one person to Las Vegas and two more to Sun Valley, Idaho. They'd apparently been waiting at the airport for about 8 hours for the weather to improve. The guy got three different weather briefings and decided to try to "pop through" the clouds against the recommendation of Flight Service. VFR Pilot are supposed to stay 500 feet below clouds, 1000 feet above them and maintain 2000 feet horizontal separation. This guy took off, got into the clouds, either didn't trust his instruments, the instruments failed or he tried to "feel" his way through the clouds. In short, he violated the law and all of his training by entering clouds and stalled the plane, entered a spin and didn't have enough altitude to make up for his mistakes.

This is not dissimilar to what JFK, Jr. did - in fact, it is almost identical to what he did.

Here's the NTSB report on the flight in LA:
[link|http://www.ntsb.gov/ntsb/brief.asp?ev_id=20030630X00971&key=1|http://www.ntsb.gov/...30630X00971&key=1]