The folks at Article Marketer publish an interesting document which they call the Article Marketing Best Practices Guide.
This guide highlights one of the major differences between Article Marketer and Article Pool.
At Article Pool, my articles are accepted into their system quickly and easily. At Article Marketer, most of my articles are rejected two or three times for failing to comply with Article Marketer's requirements.
On the face of it, this is really annoying. In the bigger picture, it could be worthwhile -- if those requirements help my articles be published on more destination sites.
The guide presents some interesting data points which may be helpful whether or not you use Article Marketer's service. The list of items which can cause an article to be rejected is amazingly extensive.