So I "upgraded" to iOS4 against my better judgement and I already am extremely pissed:
1. I had to restore the phone to stock to get my data connection - managed to save my contacts but all my SMSes are gone. Seriously, there's no way to sync them with anything... Really Apple? I lost like 300 SMSes, some of which were important to me
2. The "multitasking" is a joke. I logged in to BeejiveIM, closed the app. Asked a friend to message me a few minutes later. I got the push notification, I opened up BeejiveIM but the app had to log-in to the servers anyway which takes like 5-10 seconds! Before, with Backgrounder, I was logged in the whole time and the messages were received the moment I selected a friend. With the way Apple does it, there's no workaround unless they write an extra API for the IMs... This is just sad.
The OS is snappy and fine, but so was my JB 3.1.3...
What else? My browser - Atomic Browser. Safari on the iPhone sucks balls - no fullscreen for example, also wasted space with the address bar which you cannot hide, the lower bar is too big and unnecessary, no proper tab support, no gestures, no ad block - Atomic Browser solves all that and more! But now, when I switch away from it and switch back to it, it reloads the pages again, every tab... Since the app is not running in the background anyway :/ Hopefully they will solve this somehow. I can't stand using Safari, it's so bad. AB is perfect.
In general I am very disappointed with the update. I lost so much compared to my JB 3.1.3, I don't want to use the phone now... Hopefully a JB will show up FAST and I can get my full backgrounding, task switching (with the awesome Pro Switcher), system wide gestures and SBSettings back...
EDIT: Using a 3GS with 16GB
EDIT2: Let's not forget about 3G Unrestrictor for YouTube, App Store and the videos running in the browser. The video and sound quality is so bad when those apps think you're on 3G (or won't allow things, like the app store for items over 10MB). It's just sad.