If you have significant lag between writing JPG and RAW then either your camera doens't have a very large (or good) memory buffer in it or (more likely) your memory cards are very slow. I only use 80x or higher memory cards for my camera - sure they cost a few $$$ more but there is a major difference in speed to those $14 1GB SD cards.

Case in point - I accidently used a slower kingston SD card during a recent shoot and couldn't understand why after a 10 shot sequence.. the camera wouldln't let me take any more.. then I checked the memory card.. switched it out for my normal high speed card.. and the problem went away. Those cards cost a bit more (like $10 more.. no biggie) but the difference is very viewable.