Find out how big your Google account is (how much data Google has on you)

https://www.google.com/settings/takeout/

Have it create an archive, and it'll tell you the size.

Mine's currently at 777mb and counting.
EDIT: Suddenly 2.67gb

125.5 mb

looks to be around 20mb

How is google ever going to target relevant ads to you guys if you aren't hoarding more data on their servers?

1.45 GB so far.

Finished at 2 GB.