Macgasm brings us word that Twitter has expanded the in-page previews on its website to include iOS App Store app details. Although originally designed to do inline previews of made-for-Twitter image services like yfrog and TwitPic, Twitter has been expanding the concept in recent months; it now includes Flickr images, YouTube videos and images from the insanely popular Instagram service.
The preview for the App Store is quite detailed; as you can see, it includes the app icon, description and screenshot. If you haven't disabled iTunes opening automatically for web previews already, this might help prevent those annoying and unwanted "Aargh! Why is iTunes open now?" moments.
Two notes about this feature: you'll only see the thumbnails on the "new Twitter" web interface. They don't work on the old site, nor do they work in any Twitter clients -- including the official ones for Mac OS X and iPad. Secondly, the previews seem to be only for iOS apps; for whatever reason, Mac App Store links don't preview.