I am one of those 'remnant' dial-up users. It serves as a constant reminder to develop tight and smart.
All those sidebars, ads, and scripts loading and loading and still waiting on some third party script(s) with not a bit of content showing...immediate 'back and gone'. Making me wait does not increase my ad awareness just my bad design awareness.
I see three concerns (one upping tedster):
* the page HTML: the only times I've seen a site-wide problem is with some horrible CMS or HTML generator creating unbelieveable unnecessary code crap. Almost always nested tables with in-HTML presentation, i.e. font tags, etc.
* the external first-party images and scripts: not optimizing images for the web and running scripts before page load are regrettably common.
* third party scripts: analytics and ad programs are the biggest offenders frequently grinding away holding up content appearance sometimes until page timeout. Yes I know it is not a 'size' problem but poor scripting design really is an even bigger one.
As tedster mentions source ordered code is a life saver on dial-up, as are optimised images, having an absolute minimum of client-side scripting and running as many as possible last. Your code can be tight but a poorly designed or placed script can negate all your optimising.
Indeed the script problem is so widespread I browse with js off. Which highlights usability problems on many sites...