Still have the same problem with a new installation of Avast (which cured my registration problem see other post)
The other problem (registration) may have been contributed to by improper uninstallation previously and I wanted to see if this uninstall/install
using the Avast uninstall feature (which corrected the registration issue) impacted on this issue
The new installation automatically enabled the Web Rep extension in Chrome.

If the Web Rep extension is installed in Google Chrome
then on starting Google Chrome, my Ram goes from 2.3GB to 10mb for a period of time (one to two minutes) and then slowly returns to 2.2GB
during this period nothing can be done on the computer (of course, no memory)
This occurs on every startup of Chrome (testing was done to see if it was just a startup issue)

If I uninstall the Web Rep in Chrome
when I start Chrome my memory goes for 2.3GB to 2.28GB and there is no problem

Am on iMac 12.2 (mid 2011) 3.4Ghz Intel Core i7 with 4GB of RAM running Mountain Lion 10.8.3

The solution as before is to disable the Web Rep extension in Google Chrome