Few days ago I tried to test usability of Sharepoint 2010 on iPad’s Safari. To be honest, there is about 99% of compatibility with iOS 5 mobile Safari. But there is small amount of incompatibility with Business Inteligence components.
After a bit of browsing i found that these problems have been solved in 2011 december CU for Sharepoint. More about fixes can be read here: http://technet.microsoft.com/en-us/library/hh697482.aspx