I'm currently using an EnGenius ECB3500 AP and a WRT54GL (w/ DD-WRT) to bridge my parent's house and my brother's house. About a 600ft span with a cluster of pine trees in between. Have a Cantenna located at my brother's house and a couple of high gain omni-directional antennas at my parent's house. The signal strength stays around 40% based on what DD-WRT is reporting.
Have had no stability problems with this setup and my nephews even play their XBox 360 over the wireless bridge.