My girlfriend bought a centrino (1.4 banias-130nm ). I think the 1.7 would be the Dothan (which uses even less power)? It runs very cool even when it is running at full speed (not full load, just at 1.4Ghz). Almost all the time, it lowers the clockspeed to save battery power. I have seen it go down to 95MHz
Usually it is in the 125~300 range. I have heard the cpu fan *twice* since august, and each time it ran for only about 1 min. It has a teeny tiny aluminum heatsink, by comparison my friends P4 laptop has a three times as large all copper heatsink. The fan runs every time you click something. It is horrible, really stay away from the P4.
As for the performance, my girlfriends machine was the cheapest centrino at the time, so only 256mb ram. Can't say its excellent, but its not bad. It is the first laptop that I don't get frustrated while using. (which is saying a lot, I am very impatient.) I was under the impression that it was fast--until the ram ran out and it had to swap. Stick in another 256 and it would be ok I think. Although I am using an Athlon 1.3 (w 512ram) at the moment so take my words with a grain of salt!