Cooking from room temperature or directly from chilled
Many support the theory that it really doesn't matter what temperature the meat is prior to cooking. It's the meat's internal temperature that's the important part in determining doneness.
Several chefs do recommend bringing raw meat to room temperature before cooking. However, you don't want to let it sit at room temperature for very long since bacteria grow much faster at room temperature. This is how food born disease comes to be.
Greater consensus seems to be when roasting that it is best to allow meat to come to room temperature before cooking it. The difference it makes: if you are oven cooking, the oven temp will not be reduced by cold meat and have to come up again to where it needs to be, dropping the oven temperature with cold meat can spoil or diminish the final result. Secondly, the meat will seize, be 'shocked' if you take it from a cold fridge or freezer and put it into a hot oven or sauce - the muscles will contract and become tougher.
Cooking meat from room temperature will give a more even cooking. Roasting temperatures given in cook books for roasts are based on the meat being at room temperature. Bacteria are more of a concern if the meat's been frozen and how it's thawed.
You should always allow meat to thaw in the fridge, then let it set out for an hour or so at room temperature (but not near a source of heat, e.g. radiator). Frozen meat that has not been thawed out fully before cooking may require longer cooking time to ensure core is done.
The Food Standards Agency advice on cooking meat recommends:
Cooking food until the core temperature is 75C or above will ensure that harmful bacteria are destroyed.
However, lower cooking temperatures are acceptable provided that the core temperature is maintained for a specified period of time as follows:
60 oC (140F) for a minimum of 45 minutes
65 oC (149F) for a minimum of 10 minutes
70 oC (158F) for a minimum of 2 minutes.
Meat thermometers are available in most kitchenware departments..
It will greatly help with flavour and tenderness if you allow meat to rest after cooking.