I'm in the market for a slim travel charger for my T61 - I'd like to get something along the lines of 120W - since I have a feeling I'll be getting a W510 upgrade later this year

I've found this one Kensington Lightweight, Slim line 120 Watt DC Notebook Power Adapter for PC Laptops would this one work or could someone recommend another one?  A web site link would be appreciated

No Lenovo laptop is officially compatable with any chargers that are not 65w or 90w. Perhaps you are mistaking watts with volts?

I have a W510 and the charger that shipped with it is actually 135 watts.  I have read other places on this forum that the 90 watt charger will work for charging the battery.  I don't know if it will work for powering the machine during use.  Haven't tried it.

As for using a non-Lenovo charger... my personal preference would be to use the 135 watt charger recommended by Lenovo.  I figure why risk ruining a $3000 laptop and possibly voiding the warranty to save a few bucks on a charger?  Again, that's my personal opinion. 

I have a T500 and it works fine from the cord or the battery with a 90w charger. As for voiding the warrenty you already do that by using a non-standard charger. If it is not a Lenovo/IBM charger then you are going to be in a jam. As for the wattage. Higher wattage chargers suck more from the wall and charge the battery faster. They really don't do anything else.