Ok.
You hopefully don’t care about IE6: http://stommepoes.nl/tumblr/ie6.png png’s with alpha transparency, likely double-margin float bug (but didn’t check).
Your tag text under each photo: has a font-size larger than the line-height. Other browsers let the text overflow, but on my IE7 it’s getting slightly cut-off: http://stommepoes.nl/tumblr/tumblie7.png see the “g” in photograph"
http://stommepoes.nl/tumblr/tumblie72.png this is the <ul> itself getting highlighted… too small.
On the smarter browsers, a little blue thingie appears on :hover of the main menu. It does not appear on any IE, but an IE-user would not know it was supposed to be there (so, debatable how much you want to fix this). http://stommepoes.nl/tumblr/tumblie7menu.png Home is being hovered. IE8 also does not show the blue things.
I did not see if you are resetting margins and padding on lists, but it’s pretty common to see that one browser adds left padding while another adds left margin on lists (to make room for the bullets). Target that main menu specifically and remove any margins or padding that you did not explicitly want. This should make everyone the same.
I am not sure, but possibly IE is not showing blue things because some element is not tall enough to show them: http://stommepoes.nl/tumblr/tumblff3menu.png however this is hard to tell because your code is invalid:
<li><a href="/archive"> Archives </a></li>
<form action="/search" method="get">
<input type="text" name="q" value="" class="box"/>
<button class="btn" title="Submit Search">Search</button>
<!-- <input type="submit" value="Submit" /> -->
</form>
</ul>
A form cannot be a direct child of a ul, therefore it’s rather nice that browsers have still managed to figure out what to do with that.
You can make this legal by wrapping a <li> around the form. The form also is required to have a block child directly (you start right out with an input which is inline-block), so this is also illegal but I’ve seen so many of these that I know this is never going to cause you a visual problem. However, valid code is happy code: throw a div inside the form to wrap around the inputs. Fieldsets are overkill for little forms like that.
</li>
<li>
<form>
<div>
<the inputs>
</div>
</form>
</li>
</ul>
Also you see the form is on a new line. This is only happening in IE6 and 7, not IE8. This seems to be because the form is too wide to fit, and is dropping down: http://stommepoes.nl/tumblr/tumblie7form.png Let’s see if it gets any better after making the code valid.
compare to Firefox: http://stommepoes.nl/tumblr/tumblff3form.png
The width seems to be the culprit here, but whether it’s due to some browser default of form padding or not, I didn’t check. It’s ok to remove padding manually or in a reset from forms and fieldsets, but do not remove padding from form controls such as labels, inputs, selects or textareas.
form {
padding: 0;
}
All in all, not a disaster, you just really want that form to be on the same line as the links. The links do react on :hover and like I said, blue thingies are just an additional feedback tool that looks cute, but IE users are using an inferior browser… they practically choose to get inferior web pages : ) unless you consider it worthwhile to hunt down the exact cause of blue thingies not appearing in IE (this can be fixed).
Unless your reports from others mention some other buttons somewhere… nothing else jumped out at me.