There’s a variety of mildly annoying things about V3 of Google’s Contacts API (lack of control over which fields are returned, basically non-existent sorting ability, use of oauth bearer tokens; also they seem to be confused about their supposed mitigation of the confused deputy problem: validation does not actually seem to be required, nor does this in any way prevent an attacker from stealing the token and doing whatever they like with it).
One of the most annoying “features” is the undocumented rate limit when requesting images for a user’s contacts, each request of which must be authenticated. The rate limit appears to be around 10/s.
I wrote a lightweight jQuery plugin that will help you avoid the 503 errors that Google’s API returns when you begin exceeding this limit.
The github page has basic implementation details.