I’m doing a complete rewrite of this post as I found a better (cleaner) way to do this via an app. My initial post was using an app called Tweetcaster. It worked well enough and offered a free version, but there were some quirks with the filtering that made it a bit cumbersome. This way is MUCH easier.
Step one: Acquire iPhone. Go download Echofon for Twitter (available in Free or Pro versions – difference is no ads in Pro). Once you have your account setup in Echofon, do the following:

- Click Menu in the upper left.
- Then Account Options at the bottom.
- Select Mute in the middle.
- Under the Client section, click New Item.
- Enter “foursquare” as the new item (no quotes).
- Follow the upper left breadcrumbs back to your timeline.
- Done.
That’s all there is to it. Now you can enjoy a check-in free timeline! You can also filter out anything else you want based on it’s application. For example, to filter Gowalla checkins, just enter “gowalla” as the Client – since it is the Gowalla app that sends those tweets.
You can also filter tweets on your desktop using Tweetdeck as well as on twitter.com using Greasemonkey and a simple script!
By the way… if you find yourself swamped with checkins from your friends and do not want to have to filter them all out – you may also consider suggesting to them to not share every checkin to Twitter in the first place.

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