Some people are having problems, but many people (on various carriers) are not.
It's unclear how many are having problems that are actually due to the update, & how many could fix their problems by doing a factory reset. Then of course, some problems might even be due to an app.
If you do decide to update - if you have any issues, make sure you backup your data & do a factory reset. If problems continue, start looking at the apps on your phone before declaring Lollipop is the culprit. There are a lot of people who are happy with the update