I start comparing AMD chips at 700MHZ, since that's the fastest .25 part they made:

Model 1 .25 Micron Aluminum 700MHZ  ->  1.6v  33   Amps Typical power  45    Max power 50

Model 2 .18 Micron Aluminum 700MHZ  ->  1.6v  24   Amps Typical power  35    Max power 39

27% current drop at same voltage

Now Intel: (.25 part has separate listing for power used by 512K cache: 1.6 watts 
- cache power use clearly isn't a major issue)

PIII    .25 Micron Aluminum 600MHZ  ->  2.05v 17.5 Amps Typical power  34.5    Max power N/A

Added 256K on die cache

PIII    .18 Micron Aluminum 600MHZ  ->  1.65v 13   Amps Typical power  15.8    Max power N/A

Voltage down 20%, current down 26%

Now here's what happened when Intel went from .18 to .13:

PIII    .18 Micron Aluminum 1130MHZ  ->  1.75v 22.6 Amps Typical power  37.5    Max power N/A

Added another 256K on die cache (total now 512k)

PIII    .13 Micron Aluminum 1130MHZ  ->  1.45v 19.4 Amps Typical power  27.9    Max power N/A

Voltage down 17%, current down 14%

And just to double check, here's when Intel went from .35 to .25:

PII    .5  Micron Aluminum 266MHZ  ->  2.8v 12.7 Amps Typical power  N/A    Max power 38.2

PII    .35 Micron Aluminum 266MHZ  ->  2.0v  8.4 Amps Typical power  N/A    Max power 19.5

Voltage down 28%, current down 34%

Also interesting, here are some power reductions due to core changes by AMD:

Model 4 .18 Micron Al or Cu 1000MHZ ->  1.75v 34.6 Amps Typical power  48.7  Max power 54.3

Model 6 .18 Micron Copper   1000MHZ ->  1.75v 26.3 Amps Typical power  41.3  Max power 46.1

Current down 24% at the same voltage