I haven’t had any problems with it, in fact I have disabled system restore on my XP Pro system as I don’t feel it is that reliable (don’t do this unless you have something to take its place).

On my win7 netbook, it still has system restore enabled and I haven’t had any problems, creating new restore points or clearing old restore points, etc. This is with avast 6.0.945 and previously with 5.1.889.

Since you don’t say what avast version you are using, nor the versions that you are talking about were they are having/had a problem.

There was a period in one of the avast builds that there was a problem and disabling the self-defence module allowed it to be used, but that was resolved in another program update.