Borderless printers can be ideal for making posters. They usually have photo quality output, and their prints are easy to piece together to assemble a poster (no margin trimming required). The problem with borderless printers is that they can cut off part of edges of your images. When you have many tiles making up a poster, this can have a bad effect on the final result.
Digital Camera Poster Creator solves this with its 'Edge Calibration' feature. You print out a test print, and then tell the software how many lines you see on each edge. Digital Camera Poster Creator then compensates for the printer's edge cut off. The result is a seamless poster. See the different that 'Edge Calibration' makes: