I modified my POGO-P21 by adding an eSATA connector on the back, and I got an SSD and a Vantec NexStar 3 enclosure.
The enclosure can do eSATA or USB, and gets its power from the USB connector. The instructions (http://www.vantecusa.com/system/application/media/data_file/nst-260_user_manual-n1.pdf
) say that if you want to use eSATA, you need to plug the eSATA cable in before you plug in the USB cable; otherwise it defaults to using the USB interface.
This causes a problem when booting the Pogoplug, since you would have to plug in the eSATA cable, and then the USB cable, all before the Pogoplug looked to see whether there was an attached eSATA device to boot from. And it would not work at all on an unattended reboot.
Luckily, the NexStar 3 has a DC power input, even though it does not come with a power adapter. (It appears that the NexStar 3 3.5-inch enclosures come with a power adapter, but the 2.5-inch ones do not. I guess this makes sense, since most 3.5-inch enclosures will be stationary, and a lot of 2.5-inch enclosures will be travelling with laptops.) You can find the power adapters on the 'Net; here is one source:http://www.powerpayless.com/5v-power-adapter-for-vantec-nexstar3-2-5in-esata-hdd.html
The NexStar 3's are sleek little enclosures, and mine has been working fine, but if you get one, order a power adapter in advance, so you don't get it home and then discover you have to put your project on hold till the power adapter arrives. (That is very disappointing if you are into instant gratification.)