Is there a way to leave comments (personal notes) in a composition?

I often include text layers set as guide layers. They show up in the comp but they do not render. I also use markers all the time. When I am first starting an animation project I might also include storyboards set as guide layers to help me position things. All of these guide layers can be set to the same layer color, made shy, then turned on or off with two clicks by using the select label group option in the timeline and clicking the eye on one of the layers in the group. 

There is a comments column you can enable in your timeline, but making layer markers and composition markers and adding your comments there (as Mylenium suggests) is much more likely to be noticed since many people keep the comments column hidden.

Marker comments, possibly, but overall it's pretty much just as unintuitive as using text layers. A long time ago someoen had developed a bunch of scripts and a plug-in to do exactly what you want, but i doubt this stuff is still around and if it is, it may no longer be compatible. Feel free to comb through AEScripts.com. Maybe it turns up.

Mylenium