Don't get me wrong, its obvious I like to keep a detailed record of my results over time.
However, what I have noticed is that during a session, I really don't worry about where i'm at - whether i'm up or down, it's not really important to me. This allows me to play each and every hand on its own merits, combined with any reads on my opponents.
I suspect that if you did start worrying about your progress mid session, then it would inevitably impact the way that you played your hands. Even being on a hot run, and then being tempted to play more hands than usual is a form of tilt to be avoided. Thankfully for me, I have avoided this form of tilt, as well as the other form when you get hammered by several bad beats, and i'm sure it has served me well.
The only points at which I really start checking how i'm going at the tables is if I fall below the 12BB mark in my current stack where I will always reload. If you're less than that you can't cap every street, and may potentially be losing value if you hit a monster. The second point I check how i'm going is basically as I close every table at the end of my session to update my tracking spreadsheet.
In my 20 minute session last night which was spread mainly across a couple $2/4 tables, briefly a $3/6 table or two and a couple $1/2 tables I had the general feeling that I was doing okay but not great. It's kind of a nice surprise when I close down my tables and realise i'm up about 10BBs at all levels (with a 20BB gain on one $2/4 partly offset by a 10BB loss on the other).
On another note, my BB/100 on Bodog at $1/2 has finally moved back into the green at 0.00BB/100. Its funny that I can run like that over 34,000 hands ... and then run at 2.5BB/100 at Fulltilt over 30,000 hands, when i'm actually table selecting a lot more on Bodog than I ever did at Fulltilt. I guess that is variance for you, and my actual skill level is somewhere in the middle of those two.
Current bankroll: $19,000
July time played: 6h30m
July profit/(loss): $450