Floats are fragile and I hate to rely on it for my positioning.... good thing they have position: I use position 90% of the time to build sites.
A lot of the CSS that I see out there is so div heavy, it's the same as using tables. Try to use the least amount of divs. Don't forget that every standard tag can have css applied to it...
I didn't see this tip out here so here's my 1 cent
Code:
h1#branding {
width: 200px;
height: 200px;
background: url(../images/banner.jpg) no-repeat;
display: block;
text-align: -9999px;
}