This is the update :-
Actually 5-6 blasts have taken place & not 4.
2 bombs have been recovered & diffused. Police are still searching the area for more bombs which they suspect to be.
The bombs were not very crude but had detonators & timer devices in it. It is only that high power explosive like RDX or C4 wasn't used, because of which blasts weren't very big.
And if you see case of Delhi, there too small blasts took place first & after few days, major blasts took place. Who knows this can be just practise session for terrorists ?
Not to forget that Pune has one of the max no. of IM operatives in India, especially in areas of Kodhwa & Mohammadwadi.