Benefits:

1) Just need HTML5/CSS3/Javascript skills along with basic knowledge of Objective-C or Java..
2) Single code runs in all platforms (iOS, Android, Windows 7, mobile web) which makes our lives easy and saves lot of man-hours.
3) You can easily create build files(.app/.apk) for testing in itouch or iphone or in droid phones.
4) You can still take advantage of distribution and integrated payment via the App Store or Android Market

Drawbacks:
1) Poor performance while interacting with device parameters like camera, folders etc. For developing games its also a pain in hybrid platform. You can implement caching or leverage some 3rd party solutions (i.e. Sibblingz) for native graphics acceleration but for the most part a native app is much faster/smoother than hybrid web app
2) UI is always been a problem with hybrid app. You will miss lot of prebuilt effects for touch/scroll. While working with native app you can bring those effects easily. Now a days, jquerymobile brought some fresh air though for adopting effects in hybrid environment.