I have both the japanese "dot-s" things (luigi set) and a set of pixelblocks.
Although the dot-s is limited to the 16x16 pegboard, you can always add on more.
Pixelblocks are a cool idea in concept, but the way the blocks link together just doesn't work out too well.
Let me know if you guys have any better experiences with these - I'd like to know how to use them or if I got a bad batch or something