Got mine yesterday and I can honestly say this was a plesant surprise.
Dalvik Turbo is the key to making this fast. I rooted mine, removed all the crapplications from it, and then installed Dalvik Turbo.
Honestly, this thing is about 40% faster than it was out of the box. Don't mess with overclocking, it's not even worth it compared to Dalvik Turbo. It still is slow at bootup. It takes about a minute after loaded to get fully up to speed.
I threw out the ereader and cruz market grabage, and replaced them with Google Play and Kindle for Android.
Youtube plays HQ content at full framerate, all of my HD videos play fine so far, pandora streams fine while multitasking.
The SD cards that came with it are indeed class 4, I will be swapping that out for a class 10 16GB in a few days.
The caveats I have found so far:
-Slightly ugly (but feels sturdy)
-Still not as fast as a $400 device
-No Angry Birds
-javascrapt can't be used in any webbrowser, it will crash it.
If you can live with these, the device works great. It is a much older, slower device than what is available, but this only cost $50. It has a much better price/performance value, which makes it twice as good IMO.
Oh just FYI, the difference between the T103, T104, T105 is where it was originally sold. There is no benefit to having one over the other.