For those who drive 50 to Lake Tahoe from Sacramento, these are the spots to watch from my experience.
Eastbound at Hazel Ave. (Exit 21); CHP on right shoulder near on-ramp, commonly see cars pulled over between Folsom Blvd. and Prairie City Rd.
Westbound at Prairie City Rd. (Exit 25); CHP shooting from on-ramp.
Westbound at bottom of Bass Lake Grade (about a mile after Bass Lake Rd. (Exit 32); CHP in median behind hill
Westbound just after Cameron Park Dr. (Exit 35); CHP on right shoulder on blind downhill right curve. Particularly nasty - zero reaction time. Watch brake lights on cars ahead.
Either direction Exits 37-43 in median. Easy to spot - just look ahead.
Eastbound after Forni Rd. (Exit 44); CHP on right shoulder as speed limit drops.
Eastbound on-ramps east of Placerville (Exits 54-60) occasionally have CHP shooting from behind.
Several small towns in the Sierras have speed limit drops (Kyburz, Strawberry). Just keep eyes open.
Airplanes are also used periodically in western El Dorado County (Exits 30-44). The planes aren't that hard to spot. Most folks just don't even look.
Edit: CHP has started sitting on Eastbound on-ramp at Bass Lake Road (Exit 32). Two sightings in past week.