Liquidity is relative. If you are looking to easily move 10 - 50k shares, 50 million+ average daily volume over three months is enough (INTC, MSFT). If you are trying to scalp around with 1000 shares, 3 - 5 million should be enough (MS, CY).
for daytrading i would never trade a stock with less than 2 million shares avg vol.... i used to see lo vol stocks have their vol and trading interest just dry up and then you get stuck holding the bag.....A stock with a heavy vol shows there are many established and vested participants.