This concerns those of you who are enlightened enough to have made their computer choice by selecting Apple Inc as a supplier. Like myself that is... I recently 'discovered' something peculiar with Apple's routers though (nobody's perfect) and wanted to share this with y'all. I am not sure my conclusions are technically accurate but you can judge for yourselves.
I use a broadband connection that is rated by my ISP at 20 Mb/s on download. It never gets there but on average it hits 18 to 19 Mb/s, so it's fine, compared to most of my bros and sisters in the US! In my subscription contract I was given four to five external IP addresses (I forget how many, anyways more than 3 that is) of which I use two by means of one Airport Extreme Base Station (of the latest models) and one Time Capsule 500G. Occasionally I got some speed degradation on the Time Capsule and some difficulty to connect to Internet at all. I always 'cured' the problem by resetting the router each time that happened (plug in and out of the power outlet) and that seemed to 'solve' the problem.
Yesterday same happened again, but this time I documented the incident more precisely by using speedtest. The Time Capsule appeared to be running this time at 6Mb/s, obviously less than 1/3 its normal average. It happened after midnight though and I thought it was due to possible ISP driven slow-down because of maintenance they often do on their servers after midnight. Also, when I performed a speed test with my other router, the Airport Extreme, it showed similar slow results as well.
This morning though, I repeated the test and the TC showed again the low speed. No good, I thought... I couldn't blame the ISP this time since they are supposed to work fine on normal daytime hours, and even more so as my other router, the Airport Extreme showed its regular high speed (19+ Mb/s). I was pinging quite a few servers in the neighborhood during the process (Brussels, London, Amsterdam, Malmo, Groningen, Rotterdam... yep, I did a whole lotta testing). Repeating the TC testing showed once more the same slow download speeds. BTW, it was only my download speeds that were affected. My upload is slow anyways (an issue for cable connections, about 512 Kb/s rated, 480 Kb/s on average).
I then reset my TC and tested again. Wundebar! All speeds restored with success! Since I am using the same physical cable connection and the signals travel physically thru the same paths to my ISP's outlet and both routers (both on the 11n draft spec, btw) are connected to the same ISP modem, and I did the tests with the same wireless MacBook Pro (latest model at 2.5GHz Core 2 Duo) after experiencing what I described, I must conclude (in my own 'low tech' knowledge of such things) that this should be a software glitch on Apple's routers... I am not suggesting only the TC has the problem though. I am sure I had the same with the Airport Extreme in the past as well but I have kept no concrete numeric proof as now, as I didn't know or use the speedtest.net at the time.
Hope this helps...