2010-04-25 More of the same + Mistakes, Mistakes, Mistakes (4 of 5)
Same as the old copy - even includes some of the old errors. That said, great concise preparation material. This+official tests and you are ready to go

2010-04-12 Really the Only Guide Available (3 of 5)
The 4th edition adds about 50 or so more problems in the Additional Topics section. There are a brief couple pages added regarding Graph Theory and Algorithms but nothing substantial. However, there are a few typos in the newly added material. One notable example is that Contraposition is mislabled as Contradiction. The 4th edition is not significantly different from the 3rd edition other than the aforementioned changes.

The main complaint regarding Leduc's guide is a lack of exercises. Having taken the Mathematics Subject GRE just yesterday as of the writing of this review, I can honestly say that the major pitful encountered by most, including me, on the exam was the time constraint - an absurd 2 hours 50 minutes for 66 somewhat tricky to somewhat impossible to solve in 2.5 minutes mathematics questions.

The best use of this guide is to serve as a nexus for your studies, and augment your studies with a lot of other books and exercises. Nonetheless , since this guide is not terribly expensive, I recommend the purchase if you don't already have the 3rd edition.