The Obsidian Pipe will automatically collect items that it comes into contact with. Applying power from an Engine to the pipe will increase the range of items it can suck by 1 block (distance has been increased to roughly 4 blocks for all engines other than Redstone Engines as of 2.0.1). Redstone Engines suck up one item per a stroke, while other engines suck multiple items up at a time. Without the engine, the items need to touch the pipe to be sucked in.
The Obsidian Pipe can also extract items out of the inventory of a minecart with a chest.
A much less expensive way to make the effective distance of an Obsidian Pipe is to use many water source blocks to make the items flow towards the Obsidian Pipe.
Obsidian Pipes will not connect to other Obsidian Pipes.
The Obsidian Pipe sucks items in a pyramid shape extending outward from its mouth, to a maximum of 4 blocks away. The largest area that can be cleared by a single Obsidian Pipe is 9 by 9 blocks, achieved by suspending the pipe four blocks above a flat surface, pointing down.