Yes you can, there are advantages but there are also drawbacks.
The advantages of using AIR, fairly obviously really, are:
1. One code base means a reduced development burden; so you can build the app once and target multiple platforms. This reduces development time and cost.
2. Reduced maintenance burden, as you are working with a single code base. So if you publish an update or need to issue a bug fix, it's going to be quicker and cheaper to do so.
3. You can target desktop, flash (browser) and html (browser) from the code base too.
4. If you don't know xCode or Java it but know ActionScript 3 then of course that could be a benefit too. Though I would recommend knowing xCode and Java before embarking on mobile projects.
5. You aren't locked into using a Mac for development of iOS apps. Which if your a PC would be a benefit (though you still need a Mac to publish to the app store, but if you are strictly a PC this won't be an issue as you can buy a cheap Mac for the sole purpose of that).
There are drawbacks; such as:
1. The app will have a slightly bigger file size
2. Android targeting is limited as the device needs the AIR extension installed, which while free may pose a problem; depends on the project.
3. Blackberry is poorly targeted, only supports the Playbook
4. No Windows Phone support
5. It takes time for API's to make their way into AIR; so you may not be able to use all of the facilities you would want to, though native extensions go a long way to resolve this.
We've created a few Apps using AIR and some with Java (Android) and xCode. There isn't much between them in terms of difficulty; I find you have to be slightly more aware of performance.
If you are worried about the quality of apps produced with AIR; if you can create quality apps then you'll be able to use AIR to create a quality app. If you can't create quality apps then you're apps will be poor regardless of whether you use xCode, Java or AIR.