Twitter recently rolled out their native image product (with other media types apparently on the way). It's a simple integration that makes a ton of sense from a product perspective... particularly for Twitter mobile. Twitter received significant attention for the launch because other services reached great scale (Twitpic, yfrog, etc).
From a user perspective, I didn't think much about it until I visited Twitter.com, conducted a search and saw the below screenshot.... and it struck me why images will / should be a core part of Twitter (beyond a clean user interface): it plays a key role in Twitter search.
Here is a search for "sportsguy33" (the Twitter handle for ESPN's Bill Simmons). Beside keyword search are now Top Images of Bill Simmons. These are arguably more relevant and timely than the text being surfaced. Ultimately, the combination of Tweeter + text + image will make for a more compelling, more powerful and more differentiated search experience: