hard to replicate business models or hard to enter businesses) I truly have no way to value a Baidu.com for example - so I think P/E ratio is useless for these.

I do pullback exposure when valuations seem to get rich (in my opinion) versus growth rates - we can see that now in Apple for example, and a few other names - while I like the companies, I just cannot put a large weighting to stocks that are this rich to growth rates.

An 18 P/E ratio in 1 sector might be expensive, whereas it might be cheap in another - hence I only compare P/E ratios among peers

P/E ratio is but one of many measures one can use; and as with most things its an art not a science. If you approach it as a science of absolutes, you will miss out on many opportunities. It is but one tool in a very large tool kit.

In general you will find most of the stocks I own as relatively cheap on full year 2008 estimates, especially in relation to their (relatively) high growth rates. Even within each sector, certain companies have major advantages which may or may not deem a premium multiple.

Below are all my non ETF holdings, sorted by sector. I've sorted within each sector the stock with the largest weighting at the top, and the farther down the list, the lower the portfolio weighting is.

Energy - Coal (2009 story, not 2008 story)
ANR 43.2
MEE 27.5
WLT 15.4
JRCC N/A

Agriculture - Fertilizer ("these stocks have run up so much - how can you keep holding them - they are SoooooOOoOo expensive". Still more of a 2009 story)
MOS 33.5
POT 19.1
CF 11.6
IPI 25.5

Energy - Natural Gas Focused E&P
EAC 12.7
XTO 14.1
COG 20.1
EOG 12.5

Solar
CSIQ 14.2
YGE 15.7
TSL 8.8 (did I mention buying value has failed me in this group? this is a management discount at its best)
LDK 20.1
ENER N/A (2009 story)

Energy - Oil Service/Drillers
ATW 16.5
PDE 11.7
CLB 22.0
NOV 17.4

Energy - Non Solar Alternatives
APWR 24.8
FSYS 32.7
AMSC N/A (2009 story - maybe)

Energy - Everything
PBR 12.9

Global Infrastructure
FWLT 18.3
MDR 19.9
FLR 26.6
JEC 24.0

Financial (not really comparable to each other)
GS 9.5
MA 29.4
BLK 20.1

Metals/Mining
CLF 16.7
SLT 10.5 (India)
MTL 8.6 (Russia) (note to self - need to add MTL exposure)
RIO 10.1 (Brazil)

Technology - Computer/Communication
CIEN 12.8
RIMM 28.9
AAPL 33.2

Technology - Internet ("crazy valuation" category, but scarcity value; no pure alternatives)
MELI 67.0(South America)
BIDU 73.7 (China)

Home Builders
GFA 9.0 (Brazil)
DHI N/A (US)
LEN N/A (US)
HXM 13.1 (Mexico)

India Banks
HDB 17.9
IBN 12.9

China (Misc)
PWRD 16.1 (gaming)
CTRP 38.7 (travel)
WX 26.2 (healthcare contract research)
SOHU 26.5 (search/gaming)
HOGS 10.0 (hogs)

All Other
DRYS 4.0 (not a typo)
CMI 14.1
ILMN 70.2