I'm not aware of the spyware issue but it sounds worrying. What is the basis for your statement other than the slowing down?
My own problem after updating the free version is that I keep getting the same reminder to 'Finish' the installation on boot-up. I must have 'finished' it three or four times now!
I've been very happy with Avast for some time, until the past couple of weeks. They are completely revamping their entire system, and it appears that are actually adding their own spy-ware to computers who don't yet order the paid-service. This is really aggravating and is making my OS and entire computer slow down to a snail's pace... it's like they are throwing viral curve balls to force users to buy a virus protection/firewall system. Not nice.