Personally, I only ever use var for anonymous types. Basically, when I have to use var rather than an explicit type.
I dislike the use of var for implicitly inferring types which can just as easily be explictly declared, i.e. :
// Yes, it's obvious that i is an int! var i = 10; // But why not use "int i = 10;". Just as many characters to type! int i =10;
Also, there are some situations where typing of the var is not obvious, at least not to me, i.e.:
var q = SomeFunkyMethodThatReturnsSomething();
Hmm.. Now I have to look up SomeFunkyMethodThatReturnsSomething in order to find out it's return type before I can know what q will be. Yes, intellisense can help, but I shouldn't have to rely on that, nor should I have to perform additional steps in order to know what type q is.
Here's another (admittedly contrived example) of where this kind of typing can be confusing:
double d = 0; var e = 0;
I don't know about you, but this makes me have to do a double-take (excuse the pun!). At first glance, due to the "code noise" if you like, it's not immediately obvious what e is here. I have to stop and think before realizing that e is an int.