Then there's the matter of the generated source code. Just go and click 'View Source' on Gmail. If your browser doesn't end up crashing, you'll be unpleasantly surprised with a spaghetti of generated markdown
The rewards for integrating with Gmail though, are large. It's where a lot of people spend their time--a large and untapped marketplace of professionals. We realized this and decided to build Connect - a replacement for Rapportive's old plugin.
This is why InboxSDK is quite frankly genius. When the Clearbit team and I sat around last year trying to figure out the best way to integrate with Gmail, we were estimating at least 3-4 months of development time just dealing with Gmail's nuances. When someone pointed me to InboxSDK, I couldn't believe my luck. All our integration problems were solved in one fell swoop, and I could focus on the fun stuff - writing product.
In the end it took us a month to get the beta Gmail extension out, and one more to ship the final version. Practically all the engineering time was focussed on the product, not the messy details of the Gmail integration--that side of things was all abstracted away by the SDK. InboxSDK saved us countless hours, and more importantly, my sanity.