A buy back is always a good thing. Simple supply and demand. If they take shares out of circulation then there are less shares freely traded - price tends to go up.
In general, when you look at stocks, the less shares outstanding the better. And of the outstanding, some are restricted or owned by insiders - what is left is the float. That is the amount of tradable shares. The lower that is the quicker the price can move up or down with company developments.