This is indeed an issue. I just spend a couple hours narrowing it down. I'm using Q1 2010 309.20, with Safari 4.0. The grid displays fine in IE 7 and IE 8.
I have 6 columns in my grid, the last being a GridDateTimeColumn. The grid displays fine until I set AllowFiltering="True" for the GridDateTimeColumn. Once I set that property to true, the GridDateTimeColumn stretches horizontally, probably 50,000 pixels. Also, the filter and date picker icons sit on top of each other. Additionally, the paging area craps out.
I've attached two screenshots. The normal looking one is with AllowFiltering="false" set on the Last Modified column.