iPhone 5 user here. I've noticed with iOS 7 b1 that it takes what feels like an eternity to get to the home screen when you hit the home button. I realize it's not literally so, but compared to iOS 6 it's quite delayed from the time you hit the button to when something actually happens.
Also, my voicemail times and dates are overlapping in the voicemail menu. Looks kinda ugly! Heck, the whole voicemail menu is broken for me, and ends up crashing the phone app eventually since everything gets unresponsive after I use it.
I'm definitely looking forward to the iPhone 5S/iPhone 6. I know this is just a BETA, but the UI definitely seems sluggish compared to iOS 6.
(Oh, and the 3x3 grid for folders now is utterly ridiculous).
The Reminders menu flashes black after you entered in a reminder + time. Tapping on the reminder (to edit it) results in a strange black flash of the screen.
Aside from the quirks and a few missteps, I'm really enjoying iOS 7. It's certainly a bold step forward.
__________________