A resource hogging modem. It is my understanding that the modems using the riser will be pulling resources from the CPU.
Thus impacting your processing power. To what extent I do not know, I do not have any practical experience. The above statement is only what I have heard and not necessarily fact.
Yeah, i have an AMR (Audio Modem Riser) slot on my motherboard, but i think it is totatlly unworth it. although for me it worked out great, cuz my AGP Video Card has a big HS/Fan on it so it hangs over the AMR Slot rather then a PCI slot, so i don't lose any PCI Slots. don't buy any AMR cards, they are not worth it.