I have had my current 98 S500 for a couple years and it has now about 90K miles. It has been basically problem free for me except the radio antenna (motor) and a few minor issues. I've also had a 93 500SEL before this one. I've had some problems with it. The other MBs we had, ML 320, C280 all had more troubles when we owned them.
I've had two LS400s during the same time I have had the S500s. The LS400s are amazingly reliable and comfortable cars. No problems with them whatsoever. All you do with them is drive them and change oils.