Go to the above page and just click on the 'Choose shipping method' select element at the top of the page.
Using Safari 5.0.3 on my desktop I just see a white field dropping down from the select box, see screenshot: http://i52.tinypic.com/348plwz.png
The same page is working fine on Firefox and IE on my desktop, I haven't tested it on any other browsers. If I use the 1.0a4.1 version of JQuery Mobile then this page is working fine on Safari as well.
I just tested this on my Safari 5.0.4 on Mac OS 10.6.7 and the select menus look fine. Really odd that you're not seeing text in the the menu. If you select a value, does the feedback work right? Just wondering if the text is white or transparent or something odd like that.
Can you also flush your cache and see if there's an update? You're a dot version behind me.
Just downloaded and installed Safari 5.0.5 and I still have the same issue. When I select one of the values the text in the selectbox does get updated. When I look in the DOM the child elements do have text in them, so I think it's very likely that they're transparant.
edit: accidentally pressed the close button :(
make sure options don't get text-indented. Fixes #1717