The pros and cons of plastic bag ban legislation are too lengthy to mention. Some of the issues regarding bin liners, degradable and compostable bags, and carry bags alternatives are mentioned in previous posts.
I think that it is important to realise that realise that plastic bags were a environmental step forward from the days of widespread paper bags usage. Paper bags have much more detrimental environmental impact than their plastic equivalents.
In fact, due the low amount of energy required to produce them, some studies in the UK have shown that plastic bags are actually more environmentally friendly than their alternatives. The real problems are the incredibly selfish and thoughtless humans among us that discard these products as litter on our public lands.