i'm afraid that glyphosate, like any opther garden chemical, does have a long term effect on the environment. Just because it becomes inert on contact with teh soil and only kills the plants with whose green parts it has been in contact doesn't mean it isn't getting into water ways and water tables or being ingested by other organisms, including humans.
I know of scientists conducting environmental research on behalf of the EU and who say it is likely to be banned in the not too distant future.
There are others who have found high levels of glyphosate in processed sugars, corn and wheat and who believe it is affecting beneficial bacteria in the human gut and thus leading to an increase in digestive problems such as Crohn's disease, IBS and even obesity tendencies - http://www.naturalnews.com/040482_glyphosate_Monsanto_detoxification.html.
I personally never buy any Monsanto products but I do use other glyphosate products where no other conventional weeding techniques work. I would advise its use but with great care, especially near water courses and do not exceed the recommended doses. Adding a drop or two of washing up liquid to the mix helps it stay on the plants you want to kill and do its work better.