Here is a chart for Wireless Channel Throughput from 2.4GHz (802.11b/g) when Microwave is on( within 5m)
As you can see, channel 1 is least affect, but channel 7~9 are most affect.
However, spectrum from Microwave was vary by object location within Microwave.
For the safe side, AP should be away at least 5m from Microwave box.
Tips,
If plasma lamp/bulb is round your AP, throughput of channel 1~10 will be dropped big time.
Bluetooth, at least 5m away
Choose channel in best practice.
1, 6, 11 – 3 channel
1, 5, 9, 13 – 4 channel