Absolutely no more than 50K.

Let me put it this way:

Speed isn't everything. It's the only thing. Your site should instantly respond to a request. If you have to wait 4 seconds until something happens, you are in big trouble.

Page size = the smaller, the better. Keep it under 15k if you can. Keep it under 12k if you can. Keep it under 10k if you can. You're getting the idea here, right?

Remember = 80% of your surfers will be at 56K or less. Keep those preferences in mind when designing.

MVied, 50k is way over the maximum.

This is what http://www.websiteoptimization.com/services/analyze/ had to say about my current project. Follow the link to try your website. Valuable info.

"HTML_SIZE - Congratulations, the total size of this HTML file is 8824 bytes, which less than 20K. Assuming that you specify the HEIGHT and WIDTH of your images, this size allows your page to display content in well under 8 seconds, the average time users are willing to wait for a page to display without feedback."

Rofl 80% of the users on dial up? That's hilarious.

Stats speak for itself. Not everyone has access to high-speed internet.
The world is bigger than just the US. Think outside the box.

That depends on your target audience. I'm well aware that parts of the world only have dial-up. So I suppose if your target audience doesn't include the US, Japan, China, or Europe, then sure, 80% of your users might be on dial-up. Realistically if you're talking about a world-wide audience, you may have 30% on dial-up. For my websites, I generally offer a low bandwidth version that's basically a minimalistic version of the site. I do that with the older generations in mind because they don't always like the fancy designs and can't read the text, but I suppose it helps dial-up users also.

Just for your information. I'm currently living in South Africa. Yesterday there was a article about a pigeon beating the internet in delivering a package. Over the distance of 80km's the pigeon reached it's goal in about 2 hours, the internet status was at 4%. That's how slow internet is here. Just informing...

Another thing that I think is being greatly over looked here is optimization and compression. If caching and compression is done correctly then you site can be a bit larger and still load faster than smaller pages.

The average from what I've read is under 100kb.

Depends on your customer profile. If they are in modern cities then a little larger. If they are on dialup then maybe smaller if possible.

There are also numerous tools to decrease page load times such as AJAX