Google just released a new set of security features for Gmail. However, you cannot turn on the "always use HTTPS" option if you are also using the older java based Gmail Mobile client for smart phones, like the Blackberry. They have written that app to always fetch new mail and post actions like delete and archive over HTTP instead of HTTPS. With Gmail's new require-HTTPS feature enabled, the mobile client will error out that it cannot fetch mail. The new version (2.0.5 as of right now), is a little quirky with this setting, but it will work with require-HTTPS enabled.
Without the new version, smart phones which can fetch content over local WiFi have a ready made attack vector. Blackberries, which route all traffic through an encrypted tunnel back to the company's BES (Blackberry Enterprise Server), would find themselves vulnerable to eavesdropping and MITM closer to the BES (i.e. the corporate LAN), or, of course, at any hop along the way from the corporate LAN through the ISPs (but ISPs would never snoop on your email ;).
With these embedded devices, how many people stop to think about which protocols these apps use under the hood? It's not like on a traditional browser, where the user can at least monitor link destinations via a status bar. I would also venture to say that not too many people worry about keeping app versions up to date-- there haven't been too many nagging update applications for the majority of smart phones, yet. Google's Mobile Updater requires the user to go in and manually check for new versions. So, it's even more imperative for these app developers to get it right the first time.
Gmail Notifier is also experiencing similar issues.