I have now completed the single player achievements in this game but there is at least one glitched achievement at present, possibly two. This is for Xbox 360, I do not know if it affects PS3 the same way for trophies.
On 20th December 2011 there was an update patch released via Xbox Live which has reportedly prevented people from obtaining the Sage achievement. This is for buying all of the books within the game, you can buy then it just doesn't pop the achievement.
Luckily I noticed a thread regarding this on xbox360achievements.org while I was mopping up the single player achievements and I had only book left to buy; the last books are expensive so I had to accrue some funds.
To get around this you can play offline and delete the title update and you can obtain the achievement as normal, this is how I did it so I know it works, however if you already have all the books you will need to wait for a further patch if Ubisoft fix this issue.
Second possible glitched achievement is for Craft Maniac which requires you to craft 30 bombs in the game. I had certainly done more than this and never got the achievement, unfortunately there are no in-game stats to let you see how many bombs you have crafted. There is a challenge to craft a bomb using each of the different casings of which there are only 4 and I had not got this even though I had used all casings. Once the patch was gone I tried again for the 30 bombs and got my achievement and also the challenge confirmed I had made bombs with each casing.
Once I had these two there was only 1 other single player achievement I needed which I got so all other achievements are possible online.