C# var keyword usage

Possible Duplicates:
What to use: var or object name type?
Use of var keyword in C#
What's the point of the var keyword?
Should I always favour implictly typed local variables in C# 3.0?

I have just installed a trial version of ReSharper to evaluate it for my company. One thing that I have noticed is it is suggesting that I change the following (made up example):

string s = "";

to

var s = "";

Is it best practice to use the var keyword rather than using the Object Type when declaring variables? What advantages does it give. For context I am a former Java developer who has just transitioned to the .Net works.

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I think it's fine to use var where it makes the code easier to read, which for me would mean that the type that var is replacing must be completely obvious.

For example, this would be a good use of var (contrived example):

var thing = new Dictionary<int, KeyValuePair<string, int>>();

However this would be a bad use of var :

var thing = GetThingFromDatabase();

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I find it helpful in some cases where the type declaration is very long, for example:

Dictionary<int, string> item = new Dictionary<int, string>();

becomes

var item = new Dictionary<int, string>();

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It amounts to the same thing because using the var keyword, the variable is implicity typed and the compiler infers the type at build time. I prefer to specify the type rather than use var in most cases, so I change my resharper settings.

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