@schwenkbl - I don't know all the internals of the WP_Http class but do think in this specific instance (since we're dealing specifically with Google calendar), bypassing sslverify probably isn't that big of a deal. I would love it if someone else with more experience using this class could help. I was thinking that I can add a global setting in the next release to disable the sslverify option if needed.
For everyone else out there, you can try changing line 40 of the gcalendar-wrapper.php from this
$result = $request->request($calUrl);
$result = $request->request($calUrl, array('sslverify' => false));
If this works for any of you, please let me know so I can roll this into a future release. I can't replicate the issue on my servers and could use the help testing this out.
@vikjohn - Glad to hear the workaround did the trick for you. The aim of this plugin is to override the color scheme or 'skin' the calendar for a site. The default Google calendar embed code doesn't allow this so I would appreciate if you give the code above a try and let me know your results.