Originally, I had my Billion 5200N (above) broadcasting on channel 8 and reception was strong throughout the apartment. However, a few months ago we started having constant drop-outs. Where it was once possible to smoothly stream videos from my upstairs server to my laptop, which was connected to my TV downstairs via HDMI, it had suddenly become a nightmare, with Media Player lagging and playing catch-up and VLC stuttering like no tomorrow.
Initially, I just blamed it on solar winds and other intangibles. For some reason, it didn't immediately occur to me to check what other Wi-Fi signals were cluttering up my router's channel. Sure enough, firing up Vistumbler revealed the once clear channel 8 was now busy with two other access points. Channel 11 (usually the recommended default) was all-clear, so I switched over and straight away noticed an improvement.
It'd be nice if Wi-Fi was fire-and-forget, and for the most part it is, but to ensure you always have the best signal, it's good to take the time every once and awhile to check the channel, especially if you live in a complex. You never know when new, less tech-inclined neighbours might move in and throw your perfect setup into disarray.