I've been using Safeway delivery for a few months and I'm generally very pleased. There are definitely times when something is out of stock but there is no guarantee if I were shopping in person it would be in stock. There is a place on the online order form where you can tell them you will accept another brand if your specified brand is out of stock or if you prefer them to make no exceptions to your specific order.
I rarely cook but I have found this service makes my life so much easier, I literally despise grocery shopping so getting bottled water and a few staples delivered on my own timeframe has been the best thing ever.
The delivery men have been professional and friendly and it saves me the misery of actually doing the shopping, loading it in the car, lugging it up to the 28th floor and unloading it again. It's been a wonderful addition to my life and I will continue to use the service wherever I live in the future.