Here we try to collect information about common issues.
For our LED Matrices we used relatively cheap 5mm RGB LEDs with four legs. Please avoid to put too much mechanical stress on the LED. In particular, don't bend the legs at the basis of the LED head too much to the left and right! To be more clear: If you drill four holes for the legs into a frame with a too far spacing between the holes you might still be able to fit the LED in with some pressure but there is a fair chance to damage the LED. The result can be a more or less bright glowing of one LED column probably caused by a short cut in one of the LEDs.
The data communication of our Universal Matrix Controller Boards is based on UART with a maximal tested transfer rate of 1 MBit (1 Million baud). Every board has one data-in and one data-out port and they can simply be daisy chained for larger matrices. In principle the total size is unlimited. But with this design you are still limited to 1 MBit which confines your maximal achievable frame rate!
Let's do an example:For one frame one RGB pixel needs 3 bytes of data. For one byte UART needs 10 bits (start/stopbit + 8 bits of data). A good frame rate is about 25 fps. To get this you need a minimum data transfer rate of 750 bits/s. Based on this simple calculation you can steer 1333 pixels with 1 MBit. This is one the edge of the specifications! To be safe you should be well below.
At the end this means if you want a frame rate of 25 fps your matrix shouldn't exceed 9 boards (or 1152 pixel)!
But the good news is that we are already working on a solution. A kind of ethernet converter in front of a string of UMCBs that can be can be connected via network switch. This is still under development (June 2012) and we still need about two month for designing/testing.