I have a client who is having awful WiFi performance. if he takes a laptop (he has two) or a WiFi device (Kindle and iPad) more than a few feet outside his office the signal can go from five bars to three. Or three bars to none, meaning it disconnects from the network. He's going nuts.
We've replaced the router (now an lEA4500 with the latest firmware). We've tried an extender (RE1000 I think).
It's a very large house on a very large lot. It's not a range issue sice this hapens within 20 feet of the router. No obvious sources of RF interference. Standard wood frame construction. No people or devices hogging bandwidth.