Need application switcher

[nekokami]

How hard would it be to develop some kind of control that can switch between two open applications, e.g. iPDF and Notes? I'm thinking this could be added as an enhancement to iPDF, by adding another icon that would start a Notes session. Perhaps the dot could be the switch mechanism.

Alternatively, displaying both iPDF and Notes at the same time with a split screen (70% iPDF/30% Notes, say) could also be very useful.

I'm currently reading a lot of journal articles and I'm expected to make notes about them. It seems silly to have to use a paper notebook or my laptop for this purpose. I've been scribbling notes in the margins, and that's useful, but sometimes just having a separate window in which to make longer notes would be more functional. (Especially as I've usually zoomed to eliminate margins and improve readability.)