~via BB (wap.rabroad.com)~
The track ball thing is good.
Another item I noticed is with BlackBerry Messenger. With 51, when typing a URL, "http://", the ":/" portion would turn into an emoticon and break the link. This occurred with sending and receiving URLs in Messenger. Though, the URL would only be broken in 4.2, as 4.1 didn't have an emoticon for :/.
It's a small thing, but noticeable nonetheless.