Looks fine, clean and simple but a bit on the bare side at the moment. I immediately saw that the horizontal navigation top right needs to be raised by 5 or 10 pixels as it's half on the banner half off on the white background.
I suspect this is a Firefox issue which is what I'm using.
I've been advised myself to replace all my <p> tags with <div> tags as this apparently solves the problem. How much of a problem you see people not viewing your site properly in Firefox is up to you.
The FireFox validator extension also says you have 6 warnings (not errors)
line 41 column 83 - Warning: discarding unexpected </span>
line 42 column 4 - Warning: missing </span> before <h4>
line 43 column 23 - Warning: inserting implicit <span>
line 46 column 4 - Warning: discarding unexpected </span>
line 42 column 4 - Warning: trimming empty <span>
line 148 column 1 - Warning: trimming empty <div>
0 errors / 6 warnings
I think you generally need more visual content, pictures, imagery, illustration perhaps?