I'll start the tips and hint ball rolling with one feature of Contact that I find few users are aware of.
In the detail view of a contact, you can right click (or ctrl-click for those of you with one mouse button) on any field and get a pop-up menu of the 20 the most common entries for that field with a count of how many times each entry is used.
So, for instance if you wanted to see what first names are most common in your database, and how many times the most common names are used, simply right-click on the first name field and you get something like this:
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The 20 most common first names would appear here with a number in brackets showing how many times that piece of data shows up in that field in the database. Clicking on one of these items automatically fills in the field with that value.
Other possible uses would be seeing at a glance, in which state or city most of your contacts reside, or quickly filling out a common company name or address. This feature can be especially useful for custom fields where you might want to standardize the way data is input. Say I want to have a custom field that describes a doctors specialization, and I can't remember if I use "Pediatrician", "peds", "Pediatrics", or "PED.", the contextual menu will act basically as a value list, allowing me to always select the exact same spelling, wording, etc.