This is a difficult one to nail down...

When loading heavy pages (a few page includes, lot's of content) we have noticed that after the actual page is rendered, the browser window is unresponsible (e.g. cannot scroll) for a few seconds... we even get a beachball...

Initially we thought it had to do with our plugin but we removed it and tried with a page with no other plugins at all.

Looks like the issue is around the timer which delays loading the comment's stuff (i.e. the editor resources)...

I think this is going to be a significant issue with big installations...

See screenshot for a timeline profile.