I finished with my GMAT chapter with the score of 680. I considered to retake, but after talking with some students, graduates, and consultants, this grade should be fine when looking at my CV.
Background:I am an Engineer with a lot of passion to Math

and therefore my weakest part was the Verbal section. Oh right.. I am not a native English speaker.
Strategy:Test1: 550: Q47 V19The first test was a total shock for me because it was nothing like I saw ever before. I took the GMAX course, which by-the-way is NOT RECOMMENDED!, and the teacher there thought me some very basic rules and miss very important rules (mostly in the SC). GMAX also provided some tests of 800-score, which were very easy, and the ManhattanGmat's tests package, which were hard. So, mostly I learned from the
MGMAT tests.
MGMAT1: 600 Q47 V26
MGMAT2: 630 Q47 V30
MGMAT3: 660 Q47 V33 (why I keep getting Q47??)
MGMAT4: 650 Q48 V32
MGMAT5: 620 Q47 V26
MGMAT6: 670 Q48 V33
GmatPrep's results were bad, but I don't remember how much bad

And this freaked me out...
Test Day:I came to the testing center very scared and shocked, and the results were not a surprise.
Test2: 650: Q50 V29I needed a new method for study, so I signed up to Master GMAT (Also very NOT RECOMMENDED). They have a web interface that teaches you the rules. Well, I finished the program in one month (one or two hours every day), and I didn't feel that I improved something... The SC questions were very easy because they always based on what they showed you before. And it was always easy to eliminate the wrong questions. The RC question were very annoying! They give you a long passage with one question (never-mind the type), and timing you for that. Can you imagine that they give you one inference question and timing you for it with the time took you to perform the "initial reading"? Afterwards they give you several different passages with also one question in each passage, and THEN they give you back the first passage with a different question!!! How annoying!!
Also very important thing about Master GMAT: currently I'm working in a Computer Security as a Security Analyst, and I found that Master GMAT's site DO NOT encrypt the traffic (Not using SSL of some other encryption). But how it can hurt you? If you use the same password to this site and to your mail account, for example, any newbie hacker can download a software and get you password!!!!! BEWARE!!!
At the end I was less stressed but still I got 650.
I took a few months off to clean my head and complete the TOEFL. And decided to retake it again!
Test2: 680: Q50 V32This time I was introduced to gmatclub

I enjoyed reading others' experiences and that motivated me! My biggest problem were RC, therefore I took the GMAT RC Pill, which is HIGHLY RECOMMENDED, and bought also SC MG, which is OK but too bad it don't have enough examples. and also RC MG which is also great.
So, I started to get great scores (700+) in MG and GmatPrep, and I didn't remember the questions. But, unfortunately I got a flu a few days before the exam and didn't practice before the exam at all. And I got what I got.
Good luck!