I started playing with it because I always thought Yahoo Pipes was cool but a bit heavy-handed for light things - and I've found myself going back to add more and more tasks. Plenty of services provide some of the functionality (Twitter alerts, etc), but require a separate signup or new login, while ifttt is flexible enough to take care of tons of different cases.

Some of my recently created tasks and the holes they plug:

* RSS feeds that aren't fine-grained enough for my needs (if there's a new item in The Atlantic's Entertainment RSS feed that matches "Game of Thrones," then email it to me)

* RSS feeds that I want to be updated about ASAP, but don't want to have to sign up for (if there's a new item for an eBay search I care about, then send me a message via GTalk)

* Lightweight Twitter alerts (if there's a new tweet that mentions X, then send me a message via GTalk)

Other cool examples of ifttt flows:

http://craigt.co.uk/blog/?p=146

http://web-mastered.de/post/4748705681/iffft-dropbox-update

http://blog.christineyen.com/2011/05/how-i-use-ifttt/

tl;dr - really lightweight, well-designed version of yahoo pipes that is genuinely fun to use.