long term benzodiazepine use did cause memory and other cognitive problems for me during treatment and for a while after the (hellish) taper. I was mostly on daytime Klonopin, but I was on Restoril and also some 'z' hypnotics (ambien, sonata) during much of the time, so I imagine those drugs contributed at least somewhat.

i do think your mileage may vary, but...especially with sleeping pills, its always a good idea to keep your use as minimal as possible, if you can.