Just my opinion. I had mono about 5 or 6 years ago and I have never felt quite the same physically. It's quite a debilitating illness that can have a very long term effect on the body and never really leaves. It's not just me, many people have had this experience as well (see Robin Soderling).
Getting mono in the beginning of 2008 explains Federer's sudden drop in form IMO and why he has never been able to reach the heights he did from 2004-2007. He has never quite gotten over the illness, but being the great player he is the man is still a slam threat. Why else would he, at the mere age of 26, have such a noticeable drop in form compared to the previous years. I know I'll probably get some flaming for this but IMO this is the most likely explanation and its amazing that Roger is doing as well as he is these days.
Compare Federer to Djokovic, Murray, and Nadal who are all about the same age(26) that Federer was in 2008. They have games that are much more physically demanding and yet people scoff at the idea of them declining. It doesn't make sense to me that Roger would just drop off like that without an explanation.
Yes, mono did impact Federer. I think it costs him 1-3 slams. Kind of funny how the non-Federer fans don't think this is viable. Pro athlete with a major virus should continue to play at peak form - no sissy excuses. Sorry, that's stupid.
I also think age started catching up with him at about the same time.
Shape the placenta as follows: place a single row of tracta along the whole length of the base dough. This is then covered with the mixture [cheese and honey] from the mortar. Place another row of tracta on top and go on doing so until all the cheese and honey have been used up. Finish with a layer of tracta. … place the placenta in the oven and put a preheated lid on top of it … When ready, honey is poured over the placenta.Some sources state that this Roman dessert continued to evolve during the Byzantine (Eastern Roman) Empire into modern baklava. In Greek the word plakous (Greek: πλακοῦς) was used for Latin placenta, and the American scholar Speros Vryonis describes one type of plakous, koptoplakous (Byzantine Greek: κοπτοπλακοῦς), as a "Byzantine favorite" and "the same as the Turkish baklava", as do other writers.