I Just downloaded and tried the new Apple browser (Safari) and it works GREAT with Arabic!
I noticed there are some problems with some web sites like when a word has tashkeel it causes a word break. And there is also no way (that I could find anyway) to change the font. For example, BBCArabic.com and Elaph.com each was displayed in a different font.
In any case, this is great news! I can finally use a decent browser for all my internet browsing (I'm typing this from work on my PC so I didn't get to try typing Arabic text in Safari)
Go to Apple.com and download it now!