The only mistake of PS3 was the fact it was ahead of its time. The cell processor was so advanced the devs are getting used to it just now. This resulted in many multiplatform titles being cut for the PS3 and left to 360 and PC only. Then the titles who were ported to the PS3 were poorly optimized for the Cell because its complex and time consuming job to reach its full potential. The multiplatform titles for PS3 are looking bad and they have technical problems of all sorts - low fps, freezing etc. All this is due to the complex of the Cell, the devs are using barely 10% of it and only the exclusive titles are showing its full power.
That was the mistake of SONY - they developed something brilliant, unfortunately most of the devs were lazy to learn how to use its full potential.
Now SONY are going mainstream with slightly enhanced PC processor made by AMD and this is a smart move because the games will be very similar to their PC counterparts (even the same in the start of the gen though).