A possible situation here may be the smartphone at the belt of my pants, and the laptop on table, in this way the distance from phone to wireless PCMCIA adapter is within a foot or 30 cm.
Since some time I keep the phone on more distance when using the laptop (at least a meter away), untill now (a week or so), no more wireless rate drops. And even less minor rate changes (e.g. from 54 to 48 Mbps).
It sounds obvious that the data signal of the phone can easily interfer with the 2.4 GHz wifi signal.
Others suffering the slow wireless problem may check out their situation.
I'll keep an eye on it for my self and keep everyone updated here.
It does not specifically have to be interference with the signal it self, it can also be direct effect on the electronic part of the wireless adapter.
Like you can hear the "GSM sound"(rattling beeps) through loudspeakers of various consumer electronics.
