I already heavily use Gmail’s filters, but this trick would greatly reduce the need to create heaps of filters for individual email addresses which I would want to group together.
Gmail has an interesting quirk where you can add a plus sign (+) after your Gmail address, and it’ll still get to your inbox. It’s called plus-addressing, and it essentially gives you an unlimited number of e-mail addresses to play with. Here’s how it works: say your address is [email protected], and you want to automatically label all work e-mails. Add a plus sign and a phrase to make it [email protected] and set up a filter to label it work (to access your filters go to Settings->Filters and create a filter for messages addressed to [email protected]. Then add the label work).
Examples of its usage here.