I'm looking to downsize the amount of "stuff" I have to make it easier when I have to move. Right now, I have a practice guitar amp, which, though it's not huge, still takes up space.
Since I usually practice with headphones (because I'm still learning, and I suck), I decided to go with one of the iPhone solutions. The two big ones seem to be iRig and Ampkit. The iRig hardware costs $35 on amazon, while Ampkit Link is $30. From reading reviews, the Ampkit Link has fewer problems with feedback and outputs at a higher level because it's powered. However, several reviews on Amazon have indicated that the hardware isn't that good, with bad 1/4" sockets being the primary complaint.
As soon as I sell my current amp, I'll probably buy the Ampkit Link and hope I don't get one of the bad pieces of hardware.