Yes I mark the terrible fish and the very solid tight players. Both are equally as dangerous in online poker rooms, the fish probably have the upper hand on WPN sites though.
Play most of my poker on ignition, which has anonymous tables, so can't really do that there...you can for each game, but it is only good for that event...
Absolutely. I started doing this obsessively during the Moneymaker promotion on ACR knowing the I would be seeing many of those players later down the road. I have continued to mark players and take detailed notes because I regularly play many tournaments. I would imagine that any player right of the causal player on the spectrum would utilized the benefits of tabbing players, right?
Be sure to mark it. This helps me a lot, together with statistics. The categories are standard: red - regular, yellow - amateur, green - fish, purple - nit.