@sygys
Define "terrible slow". I have flashed my n900 couple of times and phone app has never been terrible slow to me.

And I can most certainly say (after reading this forum quite a while) that devel & testing and also some extras app might make your phone non responsive. Even official widgets could do that. Search.

Generally saying for example that NO apps could make windows crawl or brake it because if they do it´s microsofts fault has same kind of analogy as you just pointed out. It´s computer with quite open OS in your hands.

.edit
As little workaround set phone app to be always in landscape mode. See if it helps for you.