I really like these sorts of challenges because you're basically going up against yourself. You set a number of books that you reckon you can read in year and then the widget on your Goodreads account keeps track of how many books you've read and how far ahead / behind you are in terms of percentage.
Last year I set 150 books for the entire year which I thought I'd reach without too much trouble. Needless to say I over-reached just a tad, so this year I modified my expectations just a tiny bit and set it to 120.
Bit chuffed with myself as I'm only 1 book off that, and it's November - and I know I've got about 20 books that need to have reviews written for them.
There is an option where you can reset the challenge number if you want - but I'm not going to be bothered. Just more than chuffed that I've managed to actually set a target and sometime tomorrow when I finish the latest review I'm working on, it will tick over and I can shout myself a small glass of something bubbly and maybe a good book (or 2 :) )