Hi Alan:

I think most developers go for the the 600 x 800 dimension...since this is supposedly the most common dimension.  Before I started designing my latest web site I went to a Marketing & Communication website to see what the pros do.  Here's a small portolio of sites at UM: http://www.umich.edu/~mktgcomm/websites.html

Here's an especially beautifully designed site:  http://msweb.med.umich.edu/sesqui/pressreleases/index.asp

As you'll notice, these websites have a nice design that looks good floating in a space that can be smaller or larger.  The space doesn't necessarily have to be white.  From a designer's standpoint, white space, or blank space is important; you don't want to fill up all the space.

So there's my subjective opinion..!!

Linda