Let me clarify my statement. I'm NOT advocating using any BB with 4.5 that is not finished, approved, and supplied by your carrier. Why? for the very reason you are complaining about, as is nearly everyone else (that is not a BlackBerry expert) that has upgraded. If on the other hand you know what you are doing, have patience and get it sorted, the 4.5 upgrade is fine.
If you run the OS, that came with your BlackBerry you will have no complaints, trust me I do know. Far too many people buy into "upgrade mania" and take a perfectly good BB that is working just fine and create their own problems.
Why fix it when it ain't broke? (excuse the ain't, but it's the line)
If on the other hand you have an extra BB to mess with and enjoy tinkering and are prepared for issues then your OK. You don't see experience users "whining". They share their problems, work on fixes and everything works out.
My MAIN BB Curve 8310 is still running on it's Original OS.
version: 4.4.170 platform: 2.5.0.30 And it works perfectly!
Fast, stable, a year old with not one moment of down time. I have no other phones that I can say that about. It's why I rave about BlackBerrys. It's why I have nine others.... I play around with them, upgrading etc. I have an identical 8310 with 4.5.xxx that I use for trying out different things. So I can speak first hand from experience and tell you that it's no faster than my box stock 4.2.2xxx version.
So I stand by my statement and FACT, you can always count on a BlackBerry.... Period....