How much is fair ?

During my 2.5 years in an IT firm I have seen numerous types of bond; bonds signed while joining the organization as fresher, bonds signed while going on an onsite assignment and bonds when the company pays a part for your higher education or certification. The purpose is obvious; the company wants to ensure it recovers the amount it has invested on the employee. The question of concern is the amount of the bond and the time period that will be fair for both parties. The company I worked for used the SBI guarantee scheme as mentioned previously, which was pretty unfair as we had to pay the interest component if we took loan to serve the bond. Few of my friends joined in a steel company in which the bond amount was 2,00,000 and the duration was 3 years, this type of bond completely immobilises the employee, if the work is not satisfactory or if the employee thinks of changing career he has very few options left. I have seen many of my friends eagerly waiting for the day of completion of the bond to put their resignation. More ever the company should at least provide justification for fixing the amount and the time period for the bond. With the high level of attrition, especially in IT sector, companies have to go for bonds but the question remains; how much is fair ?