When starting from scratch then learning development in phonegap is no easier than starting to learn for native android, iphone, windows phone, symbian or any other.
Best feature ever with PhoneGap is that you can write app once and deploy this over 6 different platforms: Android, iPhone, WebOS(HP Palm), BlackBerry OS, Symbian and Samsung Bada. While this multiplatform support is working and widely advertised then in reality many features are not supported across all these platforms. Personally I am missing PhoneGap Facebook plugin support which extends only to android and iphone.
Minimal requirement is internet. Even if your application does not send or receive a byte of traffic then because of internal workings of PhoneGap you must grant internet permission (android.permission.INTERNET). Other issue that bothers me is that on current implementation you cannot make camera pictures or photos without memory card write permission (android.permission.WRITE_EXTERNAL_STORAGE).
One of the most interesting plugins is Analytics this allows you to track how users are using your app. There is not such feature for native apps that I know of.
I have noticed that on popular cheaper and slower phones with 600Mhz CPU there are some performance issues with mobile jquery and phonegap, you can test it on your own phone by browsing to http://jquerymobile.com/test/. Changing pages is not so smooth as it could be. On the other hand on more expensive phones these tweaks are hardly noticeable. I made some measurements on my own and PhoneGap is ca 3x slower than native code.
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