With the advent of Megabus there are actually quite a few bus transportation options now from Las Vegas to Los Angeles. Some may actually be rideable, although nothing beats the flexibility of coming and going on your own schedule, as long as you don't mind the drive. I've compiled a list of the options at http://tinyurl.com/LA-LVSched
On the busiest day (usually the weekend), there are 33 bus options now between LA and Las Vegas, with a combined capacity of about 1,800 seats/day. X-Train will provide 576 seats a day, and about 70 flights on an average weekday from all LA area airports (LAX, ONT, BUR, LGB, SNA) for a capacity of about 11,000 people.