I don't like the idea of a spreadsheet or a ledger. That's all too serious, for me. However, I am on board with this free-flow of thought on blends as I smoke them. Pen and paper is probably the way I'll go. It'll honestly most likely end up a personal tobacco review journal. I like it. I say go for the leather bound journal OP, sounds cool.
I think it'd be fun, not something to do every time I smoked a bowl (I smoke too dang many for all that), but whenever I felt like I wanted to sit down and try to critique some tobacco it'd be perfect.
I'm also fairly new. I currently have somewhere around 36 different bulk blends in pint jars at home with at least 2oz in each. Another half dozen quart jars of bulk Virginias and Burleys, and various tins I have recently bought while on the road working I wanted to try. On top of all that, a local B&M cigar shop where I am staying has pounds and pounds of bulk McClelland Virginias in stock (I'm doing my best to remedy that).
I need to keep track because I have no idea what I'm doing and I love it. Writing sounds fun while I smoke too.