clearing notifications from the home screen seems much faster than beta 3.
I find the '-' indicator of control/notification center odd compared to the '^' 'V'. Especially at the home screen as it blends in with the background more. Then when you're actually in either of them, it reverts back to the '^' 'V'.
Settings app feels much snappier now compared to B3. Animation seems smoother/faster. Same goes for multitasking and swiping between apps. Like others have said, multitasking still seems to be an afterthought compared to how it was implemented in iOS6.
I noticed parallax on the lock screen wallpaper. Don't recall that previously and I don't see an option to turn it off on just the lock screen (have the animated wallpaper on the home screen). iPad still crashes if you change wallpaper more than once.
Tabs open faster in Safari. There's also an iCloud button between bookmarks and new tabs. I don't recall this being there previously, but it very well may have and I just didn't notice. Wish you could remove that option as I never use it.
Don't recall this before, but in the clock app under world clock, it also lists the temperature and weather conditions (rain, sun, clouds, etc) on the map of the city. That's really cool. In the timer part of the clock app I also like how the numbers are slightly magnified when they're selected. It's subtle, but noticeable.
I thought I heard someone say that messages default to First name, Last initial, but mine are still showing full names and I'm not seeing an option to change this. I prefer first name and last name, but not the middle name and/or nickname. You should be able to define how you see that person's name.
Fonts appear normal size in apps such as Pulse, CNN, and ebay vs tiny like they were in Beta 3.
Syncing still doesn't work. Gets hung up at step 6 (applying changes). iTunes also shows my 32GB iPad has 18gb remaining although I'm using about 22gb, so that's off too.
Anyway, those are some quick observations after playing around with Beta 4 for about 10 minutes. My fingers are crossed battery life will improve!