I am noticing it too. The problem I'm noticing is the ads aren't loading properly, so it is making the whole page slow. It is really bad today.
It' is slow today... I don't think it's the ads. I think it's because they have more features, more pages to open and more to click on (creating photo albums, setting themes, etc)...
Also I notice that ever so often parts seem to time out and mess up the layout on Opera. It doesn't happen all the time, but does seem to happen if I have many pages up and the browser under "stress" with a lot of cached items.
That could be a combination of my computer and possibly when the server here is under stress...for lack of a better term for badwidth usage...