The package for the core library remains processing.core on Android. Early releases used processing.android.core in an attempt to avoid confusion between the two platforms. Unfortunately, this requires all libraries—even those that make only basic use of PApplet features—to maintain separate sets of code for each. Because this would needlessly affect nearly all libraries, we've decided to just use the same package naming. This makes us cringe a little, but the alternative is perpetual annoyance at maintaining separate code bases for libraries for which only the package imports differ. In practice, there is little chance for processing.core packages for both platforms to ever collide with one another, since they require completely separate classpaths to build.
The size() method operates differently, see above.
Using createGraphics() with P3D/OPENGL is only available on devices that support the FBO extension properly, which is mostly Android 2.2 and later devices. Some others may work, but lots of the implementations are very buggy.
screen.width and screen.height are replaced by displayWidth and displayHeight. See above.
beginRecord, endRecord, beginRaw, endRaw are not available. There are no plans to include them, because it doesn't make sense to use them to export geometry on a handheld or portable device.
Registering methods (registerPost(), registerDraw(), etc) is not supported. Too much overhead for too little benefit. We'll need to bring these back in a future release.
All cursor-related methods have been removed. (They don't make sense in a touch-controlled interface.)
The all-lowercase version of arraycopy() (deprecated from the desktop version) has been removed.
The (long since) deprecated openStream() method has been removed. Use createInput().
PImage.image is PImage.bitmap, to reflect that a different object type is there, in spite of its identical purpose.
PFont.font is PFont.typeface, similar as above.
The 'online' variable is not available. It's for applets to determine whether they're running online or not, which doesn't make sense on Android, where there's no such thing as an applet.