I've asked people to check http://jonathanscommunity.com, and gotten very inconsistent feedback. In a nutshell:
Win/IE: Sometimes works, sometimes displays with horizontal scrollbar.
Win/Firefox: Appears to work.
Linux/Firefox: Sometimes works, sometimes doesn't load.
OSX/Safari: Sometimes works, sometimes doesn't load.
It's normal to have display differences due to inconsistencies in how browsers interpret CSS and so on. It's a major effort to get things to work in even the most popular browsers. Seems like about one-third of theme-creating time goes into coming up with and refining the overall look and function, about one-third into getting the many small details styled consistently, and one-third into trying to solve cross-browser problems. Of course the goal is to have the display acceptable, if not perfect according to your initial goal, in all browsers.
Things should work, of course. If a page doesn't even load, then there is a functional problem beyond style flaws.
To comment on your site, it's necessary to know exactly what isn't displaying in what browser, and to see your .tpl, .css and other files that go into making the pages. General statements aren't very useful.