General Discussion

...using in-house content, you aren't likely to see much of a difference. You're not the big target.

If, OTOH, your selling of your widget has prime ordering services (handled through a third party like Paypal or bank transfers a la Paypal, as well as credit processing), is content-rich (particularly involving streaming content or other high-utilization on-demand content), perhaps offers other non-physical services (like using a site for telecommunications intra-business across disparate physical locations) and so on, then you may see a significant downgrade in performance. Furthermore, performance that is based on other companies (like Visa.com, for instance) relies on -them- being in the faster lane as well, which means that the costs will most likely be passed on to you as a consumer of -their- product.

The real danger isn't to every individual, basic site; its that every quality basic site has two to five (to, in the cases of 'big' sites like Comedy Central or CNN, 20+) sites up-chain it relies on, and the cascading effect of slow lanes and/or price increases gets worse with each successive tier of stacked services. This is before you get into things like social media, too.

For a good look at what you're actually interacting with, load NoScript into Firefox for a short amount of time. ON each page you'll get the option of allowing each successive third-party page's scripts. See just how many each one uses. For instance, DU alone uses...3, not counting ads (which also come from separate servers from most sites, although I'm not sure about DU).