Create new worlds for updates question...

Hello,
I've just got a quick question really.
When a new Bukkit version is released, do I need to create a new world in order to fully use the newest version or will my world just carry over but load everything from it and the newest stuff?
I know it's a stupid question but when I've been doing the updates, I've been creating new worlds each time.
During 1.9 I didn't make a new world, and played for a while, then thought lets make a new world, so I did and then all off a sudden I had grass, which was confusing to me because I didn't have it before, so this is the only reason why I am asking as it's confusing me.
Also, the bukkit forums do not work on my firefox anymore, I press new post and it only says my options to watch this thread, and no option to type anything, so very confusing.
Thank you all!

 

First I'm sure you saw the post on the main page about FireFox 9 I believe. The new update does some smoothing of biomes and does some I think small changes to make biomes more defined by like "beaches". So from what I've read the biome changes will work on new chunks but I've see people say they can see it on current chunks. So I'd say no you don't have to generate a new world (I don't think).