I find harvest one of the most underwhelming cards in dominion... I mean... Itīs rarely good, itīs unrealiable, and even when you get the most from it (all 4 coins) itīs still a bit lackluster for me... Even thief, when it hitīs your opponents gold or platina can be awesome, but harvest just never is. I just think that harvest needed something more, even if little...
Itīs only useful when you, for some reason, really really need that your coin income comes actions and not treasures, mostly pirate ship, and herald games come to mind. and even then there are silly things you have to worry, like not drawing your whole deck before playing it...
I had a league match recently where I bought harvest (herald was key) and found myself mostly wishing they were woodcutters (which were also avaiable), that says a lot...