I logged into my account to track some time for work I am doing and I noticed that Harvest is now accessible through the Google Apps Marketplace.
Unfortunately this aspect of the service is only available to new users who sign up for Harvest through the Google Apps Marketplace for now. Integration with existing Harvest accounts will probably follow shortly, according to the Harvest blog post.
If you are interested in signing up for Harvest and are inclined to sign up directly with Harvest on its site, please consider using this link. It includes my affiliate code and if you sign up for certain accounts, I could receive a credit to be applied to my account.