here my observations, issues after upgrading to Safari 5.1 (from 5.0.1) under 10.6.8.
Scrolling is often choppy (with two fingers, with scroll wheel). Terribly annoying.
There is – not always, bit quite often – a strange refresh-effect when switching tabs or windows: the switched-to tab/windows goes blank for a very short moment before it comes back with its content (no reload involved, apparently just a display issue), of course terribly annoying.
Text input is lagging (like here, like now).
The beach ball is seen way too often, and way more often than in 5.0.1.
Text selection is lagging. You have to do it veeeeeerrrrry sloooooowly.
I guess, you can sum it up this way: responsability and UI interaction is not right.
This is not the case with regard to page loads, which is snappy, probably even better than in 5.0.1.
Another point: Window switching changed its algorithm back to how it used to be quite some time ago (maybe pre 5.x): The order of the windows does not get re-shuffled, but stays the way it was – so, on the one hand, you have to ‘caroussel’ to all of the windows to get back to the first; on the other hand, you don’t see (as in Safari 5.0.x) one window again and again just because you paused switching for a moment, or closed out some tab. A bit hard to describe, but I guess people will recognize what I mean.
Both algorithms have their pros and cons. I guess I like 5.1’s change back to the ‘traditional’ better, but it’s also a matter of taste, I guess.
RAM usage is pretty hefty as well: “Safari Web Content” 720MB, “Safari” 267MB, Flash Player (Safari Internet plug-in) 25,8MB – I have 2 GB RAM installed.
Text input is horribly lagging. Consider me brave to have finished this posting here.
Please, Webkit/Safari team, fix it.