My assumption was that the reason for putting in the descriptions of who did what parts of the work was because that was part of the style requirements for the journal. As for where your name is in the list - I work in the pharmaceutical research industry. Our papers usually had tons of authors, and the authorship went pretty much like this:
The person who actually wrote the paper got his/her name first in the list.
The person who was running that research project got his/her name last in the list (unless he/she wrote the paper, in which case he/she is first in the list). By running, I don't mean managing - I mean the primary scientific thought behind that aspect of the project.
If the paper is being written by a chemist and published in a chemistry journal, the next cluster of names is the list of people who actually did the chemistry on the project. After that came a cluster of names of people who did the primary biology on the project. (If this was written by a biologist to be published in a biology journal, that order would be reversed). If there were contributions from scale-up, PK/PD, toxicology, etc. they usually came next, unless that was the general thrust of the paper, or unless their work was peripheral enough to the point of the paper that it was more suitable to list them in the acknowledgements. And if there were any people that actually didn't do any work but insisted on having their name on the paper anyway (managers, directors of research, other team members who were following different leads and actually didn't contribute scientifically to this particular paper), they were in the "next to last" position.
Our chemistry teams were organized as a lab head and one to three bench chemists, and that was usually the way they were listed in the author list as well. (Similar for biology). So unless you actually wrote the paper (first author) or spawned and guided the research that led to the paper (last author), or didn't do anything at all (next-to-last author), any other position in the list was pretty much immaterial. There was no real difference between second, third, fourteenth, or twenty-seventh author.
In response to OrgoPete - we were much more restrictive about patent authorship. If you were not the single lab head who first disclosed material for the patent, it took an Act of God to get your name on the patent. Even though I worked for a huge research division, almost all of our patents only had one or two names listed as inventors. It certainly didn't include everybody who worked on the project, or even the lab heads of all the labs that worked on the project. The only way a person who was not a lab head could get their name on the patent was to demonstrate that the lab head actually had no idea the person was working on the project until it had proven successful. Then you might be listed as second inventor behind the lab head.