A bit of a different take on this...
I have a pretty generic portfolio on 4 sites (was 5 till StockXpert folded their tent) My monthly earnings have been creeping up over the last 5 years in a pretty consistent fashion despite a busy month only seeing 30-40 new images, and many months I add none. (Yes, month, not week). (links below if you wanna check them out, feel free to buy some images while there! :-) )
You can see from that the big growth has been in IS earnings. The big upward kink in that line was one of their pricing changes at about the same time I got keen and uploaded more images than my normal trickle.
SS 'peaks' after new uploads, but as has been mentioned before (on here, or SS forums??) the peaks include old image sales which is odd, but that's the nature of the subscription model I suppose.
The big peak in SS sales around Jul '08 was when I was unemployed from a 'real' job and spent a lot more time uploading images, I think I put 80 odd images up on SS in that one month.
FL responded well to the increase in images, and seems to have held the growth in income after the peak that SS saw.
If anyone else has similar records and a fairly 'average' portfolio it'd be interesting to compare them.. (Obviously with the actualy $ figures removed like mine!!)
I'm looking at spending more time this year on micros, and I've decided to start uploading some of the 'better' stuff which I used to keep for prints at a local gallery, probably not stock worthy, bordering on arty, but will be interesting to see how it goes..
Cheers, Chris H.