According to Williams:
"Interlagos is positioned at a high altitude and has ambient air pressures around 930mbar which causes an 8% reduction in downforce, drag and engine power compared to when we race at circuits at sea level."
http://www.williamsf1.com/news/view/760
And then this from Heikki:
"and using KERS Hybrid – particularly up that long hill out of the final corner – should be a considerable benefit both in qualifying and the race."
http://www.mclaren.com/f1season/2009/brazil/preview.php
So yes, it looks like KERS will be quite useful here.
The reduction in power could be a big problem for Vettel as he is using old engines now, isn't he?
[CONTAINER][pre]Driver AU MA CN BA SP MO TU GB GE HU EU BE IT SI JP BR AD
LH 1 1 2 2 2 3 3 4 4 5 5 6 7 7 7
HK 1 1 1 2 2 3 3 4 4 5 5 6 7 7 7
FM/GF 1 2 2 3 3 4 4 4 5 5 5 6 6 7 7
KR 1 2 2 3 3 3 4 4 4 5 5 6 6 7 7
RK 1 2 3 3 4 4 4 5,6 6 6 6 6 7 8 8
NH 1 2 2 3 3 3 4 4 5 5 5 6 7 8,9 9
FA 1 2 2 3 3 3 4 5 5 5 5 6 6 6 7
NP/RG 1 2 2 3 3 3 4 5 5 5 5 6 6 6 7
JT 1 2 2 3 4 4 5 5 5 5 6 7 7 7 8
TG 1 2 2 3 4 4 5 5 5 5 6 7 7 7 8
SB/JA 1 1(2) 2 2 3 3 3 3 4 4 5 5 6 6 7
SBu 1 1(2) 2 2 3 3 3 3 4 4 5 5 6 6 7
MW 1 2 2 3 3 3 4 5 5 5 5 6,7 7 7 8
SV 1 2 2 3 3 3 4 5 5 5 6 7 8 8 8
NR 1 2 2 3 4 4 4 5 5 5 6 6 7 7 8
KN 1 2 2 2 3 3 4 5 5 5 6 6 7 7 8
GF/LI 1 2 2 3 3 3 4 4 5 5 6 6 7 7 7
AS 1 2 2 3 3 3 4 4 5 5 6 6 7 7 7
JB 1 2 2 3 3 3 4 4 5 5 6 6 7 7 7
RB 1 2 2 3 3 3 4 4 5 5 5 6 7 7 7[/pre][/CONTAINER]