In regards to how far back the rows go, most of those bottles are single bottles only. I keep empty ink bottles and empty boxes behind the filled bottles. However, I do keep some duplicates. For example, I have four bottles of the Noodler's UK Series ink, The Sun Never Sets. I usually replenish a bottle once the one I have gets lower than 1/4 full, depending on the colour.
For those of you wondering about the bottles being next to the window, I usually keep the blinds shut all day in that room, so the room stays dark 90% of the time. I only open the blinds when I am filling ink sample orders (and not even all the time then), but having easy and quick access to all colours I own is a must so I can fill ink sample orders quickly.
Since that photo was taken, I've filled up most of those empty spaces with new ink.
ETA: Honestly, I don't think I have that many bottles...
Edited by paperskater, 14 June 2011 - 03:25.