Google claims that Gmail for Mobile Devices offers improved access times (reportedly up to five times faster) and ease-of-use due to technology that automatically pre-fetches e-mail messages. The company has promised other improvements, such as reduced clicks and scrolling to access e-mail; fewer keystrokes for reading, composing, or searching mail; and support for attachments, including files and photos that can be automatically resized to fit the desktop on the user's phone.
If you are a Sprint user, the article also mentions that Google has partnered with them as a distribution method. Of course, it'll run on any phone, it's just a bit easier for you Sprint users. If you haven't given Gmail mobile a try yet, it's definitely worth it.