They recently upgraded the Raspberry Pi by doubling the systems memory to 512 and overclocking the processor to 1 gigahertz and coming out with drivers to allow using the GPU as a processing resource with full floating point "hard float".
Net result is it doesn't molasses on you so much any more. It is still SLOW when compared to modern phones and tablets as it is ARMv7 instead of ARMv8 (which is the oldest arm that say Ubuntu supports).
Buy a Pi and Raspian is all you will ever get for a Linux (Debian with Raspberry Pi customizations).
However the huge fan base and many customizations make the device a good trick for a media center. The processor is the exact same processor used in the Roku lite box, so it can get the job done, but not killing fast.
Raspian Linux is pretty much cooked now and it will get ongoing support and customization.
The folks at RasberryPi will not talk about future models (tends to kill off the current model if you do that) but there are a world of dual core $4-$7 processors out there that make the $3 processor they are using now look like a stone slug.
They are also NOT INTERESTED in latest/greatest at all, but want a stable system to allow schools to buy into it for a period of some years at a very low purchase price. They would add a feature or drop the price rather than modernize the base chipset.
Here is a better unit at the same price, with somewhat similar Linux support. (don't forget you have to buy a base OS SD card and a power supply and the cables with the Raspberry Pi and all that stuff comes with this bad boy)
http://www.ebay.com/itm/MK802-Android-4-0-TV-BOX-Allwinner-1-5GHZ-A10-1GB-DDR...Just be aware that these sticks tend to change and modernize as soon as a Chinese chip maker puts out a better chip and also
be aware that not all Chinese chips have any sort of Linux support from their vendors. The MK 802 does have a lot of support though as they all use Allwinner's A10 chipset and Miniand forums hold all the needed Linux support for that chipset you can get.
https://www.miniand.com/ gotta like that hackberry board for all the extras like wifi and cat5 and such
Raspberry Pi has more support right now and better software and more programming stuff for it though by a factor of 10.
This will change soon when Linux kernel 3.77 comes out, then Linaro will have built-in support for all the new ARM chipsets and their Mali graphics systems baked right into the Linux kernel. Supported from the get go, native.
The Pi won't have this as it falls well before the v8 cut off as a "modern system". Next year the Pi falls back into Linux obscurity so to speak.
The new ARM stuff will have a world of OS systems available to it, including that semi-aborted Windows 8 RT garbage.
And remember, all the neat new Nexus products from Google have the new A-15 super chip in them and the new Mali 604 graphics, and you can put Ubuntu and Chrome OS on them as we speak.
Notice also that the new Android is pretty neat and is shaping up as a real keeper as a consumption tool. Dual booting your tablet with a full Linux OS is here now too, so you can have the best of both worlds if you want it.