Here are the numbers for Tamilnadu:
Total population: 623 lakhs; reservation 69%
(TN doesnt classify as OBC -- they break it down into BC and MBC)
Backward Classes -- pop:289 lakhs (46.2%) -- reservation 30%
Most Backward and denotified tribes -- pop:129 lakhs (20.7%) -- reservation 20%
Scheduled Castes -- pop:118 lakhs (19%) -- reservation 18%
Scheduled Tribes -- pop: 7 lakhs (1.1%) -- reservation 1%
All others -- pop:80 lakhs (13%) -- open (no reservations) 31%
Even at 69% reservations, the reservation percentages are lesser than population percentages. In rest of India with 27% reservations, its clearly evident what the ratios are. I dont have a link which gives us population-wise percentage breakdown of OBC/SC/ST/Others at the national level. If someone can find that, please post.
best references for the TN numbers are:
 Tamilnadu government policy note on BC and MBC welfare:
 Ravishankar Arunachalam's article on the mathematics of reservations:
Also, to address the example that Ashwini was talking about, take a look at the national policy on creamy layer, from the Indian govt.'s National Commission for Backward Classes(NCBC) website:
Particularly look at issue VI. Income/Wealth Test. That addresses the "economic" creamy layer who will not fall under reservation category.
Son(s) daughter(s) –The other categories are also quite illuminating in providing a picture of what the NCBC considers as privileges in the Indian society.
(a) Persons having gross annual income of Rs. 1 lakh or above or possessing wealth above the exemption limit as prescribed in the Wealth Act for a period of three consecutive years.
(b) Persons in Categories I, II, III and V-A who are not disentitled to the benefit of reservation but have income from other sources of wealth which will bring them within the income/wealth criteria mentioned in (a) above.
(i) Income from salaries or agricultural land shall not be clubbed;
(ii) The income criteria in terms of rupee will be modified taking into account the change in its value every three years. If the situation, however, so demands, the interregnum may be less.
Another interesting link from the NCBC site is the set of guidelines that determine whether a community can be categorized as OBC.