We returned from India several weeks ago and must say that if you plan on travelling to South India only, the 2007 edition of the LP South India, gives you all the - in my eyes - most up to date info you could wish for. No need to bother with the extra weight of the
India (Lonely Planet India) (an additional 700 something pages).
The LP South India is divided into parts about Maharashtra, Goa, Karnataka, Andra Pradesh, Kerala, Tamil Nadu, the Andaman & Nicobar Islands and a whole chapter is devoted to Mumbai. As usual it contains info on transport, annoyances, health & language. Contrary to common belief the LP does contain information on other than backpackers' accommodations as well.
I recommend getting your LP South India well in time before you depart. There is lots of info to highlight & digest and it helps you planning your stay, especially if you won't have much time and want to make the most of it. The LP South India certainly did help us a lot to make the most of the short time we had there!