I wasn't around for 3.x to 4.x, but from what I see in OS 5.0 vs OS 4.7 there isn't really anything hugely different.
The OS functions the same, menus the same, etc. There are a few new things, such as the applications in the options menu has been totally redone (much better too), threaded sms, better looking widgets, etc. There's nothing that's going to make you have to relearn how to use a blackberry, if that's what you mean.
It's not like going from Windows XP to Vista where you had to play the "where'd my crap go" game until you got used to it.
