Like the rest of you, I was keen to see Photoshop Express appear on the web, which it did just last week. The potential of being able to access a photo editing tool with a URL is certainly appealing.
However, the Photoshop Express Terms of Service (ToS) are worth a peek. The ToS permits:
.. you grant Adobe a worldwide, royalty-free, nonexclusive, perpetual, irrevocable, and fully sublicensable license to use, distribute, derive revenue or other remuneration from, reproduce, modify, adapt, publish, translate, publicly perform and publicly display such Content (in whole or in part) and to incorporate such Content into other Materials or works in any format or medium now known or later developed.
Ouchies.
You might want to wait a bit before uploading any of your content.
Wired has a detailed discussion in "Photoshop Express: All Your Images Are Belong to Us".