If you use the client's timezone preference to store the date and then use the client's timezone preference to recover the date at a future date, you might stil

If you use the client's timezone preference to store the date and then use the client's timezone preference to recover the date at a future date, you might still mess it up (from the user perspective). It depends on the user's intent. If they book something at 4:00pm 2 years from now, will that become 5:00pm if the timezone rules change or stay at 4:00pm. I'd argue that for most future-dated items it should stay at 4:00pm. The only way to guarantee that is store the local time. Storing UTC doesn't relieve you of timezone problems.