Do you think cloud/internet Based Ant-virus programs are effective at protecting your PC?

[froggyboy604]

Are cloud based Anti-virus like Immunet protect and Panda Cloud Anti-virus good anti-viruses for protecting a computer?

They look like good anti-virus programs for PCs that are slow like slower Netbooks/laptops, and older computers, but If I lose my internet connection then my PC is not protected because it is not connected to the internet/clouds anymore.

I guest it is also good for PC that have not a lot of hard drive space.