I don't like it when publishers move the date around several times or even once.
Thankfully, this doesn't happen ALL the time, but enough. It really sucks when this happens, especially if it's only a few short months before the original publication date. Even if it's not, you were all set to get that awesome sequel on June 9th....but what's this?! It's been changed to August 23rd! My life is over.

I'm sure the publishing companies have their reasons for doing it; I mean, I've never worked in one and probably never will. But at the same time, it's very frustrating. Especially when they push the date back a long ways.
Examples:

The Eternity Cure by Julie Kagawa - Goodreads tells me I finished The Immortal Rules on April 1st, so if the date hadn't gotten moved to April 30th, I could have had it by now. (I will not comment on the awful cover, I will not comment on the awful cover...)

Unravel Me by Tahereh Mafi is probably the worst offender I can think of off the top of my head. Shatter Me came out in November, and this sequel was supposed to as well, but it got pushed all the way to February. Granted, Mafi wrote us a lovely novella to tide us over, but still, three months?

Entwined with You by Sylvia Day (adult book) - The release date has flip-flopped back and forth for a while now. I don't think I can trust it anymore. I'll just buy it whenever I see it show up at the bookstore, I guess.
Oh well. I guess I'll just have to give my overwhelmingly large (seriously, there's no way I'll finish them all before I die, which is depressing) TBR list some more attention to distract myself from ever-changing dates.