It's not a matter of getting used to it. It's simply more difficult to deal with, no matter how long you do it. Since English is read from top to bottom, your eyes have to track top to bottom to read a post. But to scan the posts now, your eyes have to track bottom to top. So, with the normal way posts are ordered your eyes simply track top to bottom all the way down the page. But with the way it is now, you have to track bottom to top, then top to bottom for a while, then reverse direction and back up through the crap you just read and do it over and over again until you finish the page. It's not like it's a HUGE deal, obviously, but it's enough of a pain in the ass that I don't want to mess with it.
I can't even imagine out how it occured to someone to add this option to the software. It's like a publisher saying, "I know! We'll put all the paragraphs of this book in reverse order so the reader has the maximum amount of difficulty possible reading it." The only people who could possibly benifit from this setup are the people who check the boards every five minutes and only have to read one new post in a topic.
But hey, it's your place - you do whatever the heck you want with it. I'm just adding my thoughts to the thread.