The Power of "Calcualted Column" in SharePoint

By adding a calculated column to a list or library, you can create a formula that includes data from other columns and performs functions to calculate dates and times, to perform mathematical equations, or to manipulate text. For example, on a tasks list, you can use a column to calculate the number of days it takes to complete each task, based on the Start Date and Date Completed columns.
(Excerpt from the Microsoft Web site)

The best part is using [Today] & [Me] column in a calculated column by this trick :

A List Item's age : link
Days Left/Day in current Year(Birthday) link

In a note on Microsoft website, Please ensure this when using a site column of calculated type :
"The formula in a calculated site column can reference only other site columns that are in the same list or library. Therefore, when you add the calculated site column to a list or library, you must also add the site column that is referenced in the formula."

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The big BUT may come when you try to use calculated column in CAML query : Simply change the field type from "Calculated" to "Text" or "Number" or by choice
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Update:
This solution works but only for a day, as Today's value is static.
Creating a simple window service which creates and deletes a Column with name Today, does the trick. You can also create a SharePoint Timer Job for the same. Though it's a pain initially, bur it works. 
Let me know if you have any difficulty in creating such a solution