TAIns sorry for this late update.
Autosafari and all others thanks a ton for the route u had specified, it was fun driving down south.
I think every body planning to go to kerala ie say upto alleppey or further south can follow this routeas specified by @autosafari
the roads were very very good and you can relax and drive as the route is a one way uptill walayar checkpost ie entry kerala border. then I think from walayar till trishur its 2 way and from trichur to ernakulam its 1 way once again then from ernakulam till alleppey its 2 way again. Some road repair work and widening work was on at selam in the month of march 2012 but they were progressing pretty fast kudos to tamilnadu govt for the road development thats happening.
But the bad part is you end up paying a toll of around 1500 rs approx from mumbai pune highway till kerala. Thanks to some political dadagiri in kerala we were diverted from a beautifully made 4 or 6 lane road to a tiny road somewere close to trichur toll naka. I feel the toll enroute is maximum in maharashtra and karnataka, but in karnataka i felt the roads are decently maintained, so its worth.
I took a pit stop at bangalore hosur main road , the hotel was Grand krishna, pretty decent to stay and the rent was also good. attached issrikrishna group
. pls dont go inside bangalore city and take nice road to avoid city traffic.
But you end up doing something close to 200 odd kms extra. But i think that is worth. Once in Kerala you have a chaotic traffic scenario. Some drivers simply refuse to let you pass. So keep your anger in check