Here's a link to the issue for which we included the relax compiler argument: https://code.google.com/p/arduino/issues/detail?id=729

BTW, there are generic Client, Server, IPAddress classes in the core, that various implementations can inherit from to provide a common interface. It probably doesn't share as much as it could but it's something.

Sorry, there was a change in 1.0.2 that is incompatible with processors that don't have hardware serial support (like the ATtiny). This will be fixed in 1.0.3.  See: https://github.com/damellis/attiny/issues/8. For now, you can use 1.0.1 or change:

#error TXC0 not definable in HardwareSerial.h

to:

#warning TXC0 not definable in HardwareSerial.h

in HardwareSerial.h.

In the Finder, you can right-click on the application and select open. I think there's a dialog box warning, but it has an option to open the application anyway.  From then on, you should be able to launch the application normally.

We're working on getting the application properly signed so that this won't be necessary.

And can you enable verbose output during compilation (in the Preferences dialog) and post the full output here?

Hmm, if blink isn't working there's definitely some issue.  What happens when you try to upload?  What operating system are you on?  Which version of the Arduino software are you using?

Hmm... what do you see in the Device Manager for the Leonardo?  Is it an official Arduino Leonardo (others may have different USB IDs and require different driver files)? 

You don't need the FTDI drivers because the Uno uses a different USB to serial chip.  Which directory are you indicating when trying to install the drivers?  Make sure it's the main "drivers" directory, not the FTDI sub-directory.

There's an issue with the Polish translation that stops the application from running.  See: http://code.google.com/p/arduino/issues/detail?id=942 for more information.

What happens when you try to install them?

Hmmm....  the rxtx library and DLL are the things that determine which COM ports appear in the menu, so I'd start there.  Can you get rid of the custom RXTX DLL and try with the standard one? 

Also, make sure there aren't any other programs trying to scan / use COM ports (e.g. for things like cellular wifi dongles, cellphone syncing, etc). 

Can you upload with verbose output enabled (in the Preferences dialog) and post the output here?

It might be an anti-virus program or firewall is preventing access to the serial port.  Or that some other program has it open already. 

Do you see the Arduino under "unknown devices" in the Device Manager?

Josephiah: it looks like the communication is flakey for some reason, maybe the power is cutting in and out (or there's a short appearing and disappearing).  Is it possible the board was damaged somehow (either physically or with too much current / voltage)?  Do you see the same behavior with nothing connected to the board?

There is a bug in the Mega 2560 bootloader that causes uploads to fail if your compiled sketch binary contains the string "!!!" (because this triggers a serial terminal).  This might be happening by chance with this code, e.g. in an array or lookup table or just by coincidence.