Living and working in France, I've had the opportunity to discuss their national service with many of my colleagues. Most people had to serve a year in the military, although the rich or well-educated could do a two-week basic, followed by a year working for a French national company overseas, or some other area of vital national interest (a colleague worked for a year in a government nuclear physics lab).
Most people I've talked to found that their time was completely wasted, and don't look fondly back on their time in the military. The younger people who weren't involved (the program was phased out in the late 90's) are very grateful that they didn't have to bother. When this topic comes up for discussion, I normally ask people how they think conscripts affect the effectiveness of the French military when deployed abroad. One guy just looked at me like I asked him to recite Shakespeare in Swahili. Most people say one really had very little effect on the other, since they were essentially two different armies- the professional one that the government actually did something with, and the social engineering project.
The instructors and NCO's for the conscripts came from the professional army, but they mostly resented their time there, or treated it like a holiday (for a Canadian context some people may be more familiar with, imagine a crusty bigoted old reg force WO posted to a reserve regiment, with the additional wrinkle that all of the prejudices he has against the reserves are actually true- it wouldn't be a worthwhile experience for the WO or for the soldiers).
While the conscripts may not have adversely affected the effectiveness of the regular army, they were certainly a drain on the resources of the government. Based on the small sample size and unscientific polls I've conducted, I'd say that the social engineering project of conscription was a failure in France. The arguments for such a project are normally to instill our youth with discipline, citizenship, knowledge of military and world affairs, etc. Like every other society, some people have these things (with or without prior military service), and some don't, but I don't see a higher proportion of these qualities in French men (or former conscripts of other nationalities that I've talked to).