rubinetto - 9:54 am on Feb 11, 2013 (gmt 0)
Average time and bouncing rate are not ranking factors but affect the relevance of a page.
For some sites the bouncing rate is more important (informational sites for example) and for other Google consider more important the average time (entertainment sites for example).
Depending on what niche you're in, manipulating this values with the right strategy can actually give you an edge and that's why you see many sites doing that.
I don't believe is the right approach for long term business but I've implemented it with success on one of my sites and if I had an informational blog -like some of you- I'll definitely split the post in two or more parts in order to reduce the bouncing rate.