While it's nice that Google is buying wind power, you have to ask the question where does the power come from when the wind doesn't blow? Since the power apparently comes from a single wind farm, this is probably going to happen.
Also, there's a clear trend to replace coal with cleaner, cheaper natural gas. Since 2002, the MWH produced by coal has gone down by 10%, while the amount produced by natural gas has gone up by 47% (see http://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_1_1 ). Clearly electrical utilities are choosing natural gas for most of their new plants. This means less CO2 produced per MWH, as well as less water needed for cooling.