If you have a cordless phone then this would be my number one suspect. WiFi and many cordless phones operate in or near the 2.4 GHz bandwidth (or have harmonics that can interfere). Baby monitors and even fluorescent lights might cause interference too. Then again, if there are people or objects moving in front of your access point that too can cause a temporary loss of signal. It's not very likely since the very nature of the 2.4GHz and especially the 5GHz band are relatively immune from disturbances like that. But it's still a possibility.
More likely might be your system's power settings. Have you checked that you haven't enabled your power settings to turn off WiFi when it isn't being used?
Another possibility might be NIC and/or DHCP settings. Is your NIC confused or trying to use IPV6 (where there is none)? Maybe your router has it's DHCP renewal policy set to something odd. Then again, maybe your ISP is fiddling with IPv4 addresses and your routers NAT can't keep up. To determine what's going on I usually like to see if I can at least get to my routers administration page (usually 192.168.1.1).
One other thing may simply be your connection and the use of whatever "phone book" is being used to look up Internet addresses. For that, I'd be looking at changing my DNS settings. (I might suggest OpenDNS at http://www.opendns.com - their addresses are 188.8.131.52 and 184.108.40.206.)
I really can't say why any of this is happening or if those are things to even be concerned with. But at least it's a start. Hope it helps...