The only limitation I can spot is only 2 PC
I wouldnt really class that as a limitation - according to the specs it says
Internal slots are 1 x PCI Express x16, 1 x PCI Express x1, 2 x PCI,I think most new mobos now have 2xPCI plus the 2
PCIe's, so it should be plenty. If you do want to add a graphics card that would go in the PCIe x16 slot.
The processor to me seems a bit slow - but its more than adequate for general usage.
I wouldnt recommend putting Vista on it.. it could begin to stuggle with the HDD space and RAM.
But then again it does depend on what the heck do you expect from a machine that only costs around £100.. all in all a damn good buy for someone who doesnt need the additional power. Some-one like my dad could quite happily live with that kind of spec.