Picasa Web was one of the few Google services that didn’t support secure connections.
Now you can use the secure version at
https://picasaweb.google.com and be sure that no one intercepts your requests. This is especially useful if you are using an unsecured WiFi connection.
Most Google services support HTTPS: Gmail (by default), Google Reader, Google Groups, Google Search, Google Finance, YouTube (in part) and now Picasa Web.
A number of services generally support only secure connections: Google Calendar, Google Docs, Google Sites, Google Health, Google Analytics, Google AdSense and AdWords, Google Web History, Google Bookmarks, Google Voice, Google Latitude, Google Checkout.