I haven't seen anyone cover some of the undocumented filters trick you can do with Gmail. Gmail doesn't even have a "how to" on filters yet. The reason they don't have a "how to" is because it's pretty dang simple (oh yea, and its in beta still).

You can setup a filter to automatically do actions on an e-mail such as: Skip the Inbox (Archive it), Star it, Apply a label, or Move it to the Trash. These filters can be based upon a combination of: From, To, Subject, Has the words, Doesn't have the words, and Has attachment.

I haven't pushed the limited, but from this tricks 'n' tidbits page I see that Gmail currently has a limit of 20 filters.

So I offer the follow tip for creating less filters: Use "|" (OR) and "*" (wildcard) characters to catch multiple e-mail addresses and apply a general filter.

Example 1:
Starring and Labeling e-mails from specified buddies of mine. I setup a label called "Buddies". Then I go and create a new filter. The "From" field can contain multiple e-mail addresses, but not a comma delimited list like one might first expect. You need to separate each e-mail address with a "|" (pipe) which means "OR".

From: joe.shmoe@hotmail.com|Bob.Dole|geek@foo.com

The above example will catch e-mail from either joe.shmoe@hotmail.com, Bob.Dole@gmail.com (notice in my filter I didn't specify "@gmail.com", this is because you don't need the domain when referencing other Gmail users - same for when composing an e-mail), or geek@foo.com.

Click "Next Step"...

Then just select the "Star it" option, and select the "Buddies" label. Now all new messages from these three friends will be starred and labeled automatically.

Example 2:
Very similar to example 1 but now using "*" wildcards. This filter catches all e-mail from vendors I frequently make on-line purchases with. Some vendors like Amazon.com will use multiple e-mail addresses when I make a single purchase - one when I first place my order and then another when my items ship.

First I create a filter "On-line Shopping". Then I go and create new filter with the following...

From: *@amazon.com|*@paypal.com|*@ebay.com|*@buy.com|*@thinkgeek.com

The above covers a few places that I purchase items from - your list of course will vary, but you get the idea. And depending upon how avid of an eBay seller/buying you are - you may want a separate label.

Personally, I "Star it" and apply the "On-line Shopping" label to this filter as well. Then, when an order arrives and the transaction is complete, I manually unstar and "Archive" the e-mail, and it will always be available by the label search.

So, I hope I was able to open a few eyes to the possibilities of using filters. Now... to test Regular Expressions in filters???