Great discussion!
I'm the owner of the site and I've been browsing BYC with this account that has all the same ads, etc. as all other members.
I haven't experienced any slowness at all. We're also on top-end servers that are only using about 1/2 of their potential at the most busy times, so I don't think that's the issue.
I am using the site on Chrome and Firefox. I avoid Microsoft browsers like the plague, but that's just a personal preference.
Since it isn't a sitewide problem... at least with all users and all browsers, the problem will be specific with the combo of what's on your system and how it's interacting with our system. It could be anything from the browser to addons / extensions / plugins, etc.
We're constantly trying to tweak things to make the user experience better for everyone... it just gets tricky with the infinite number of variable combinations and difficulty duplicating the issues reported that aren't consistent for multiple members.
Could you try another browser on another computer as a test to see if it makes any difference? That will help us start to isolate the problem.