thats a bad idea in many ways.

how bout if they need to access your site from work/home or they change their NIC or get a new wireless card, or they get a new wifi router/gateway...  lots of extra overhead IMO to keep up with that.

is there a big reason why you think people would have multiple accounts?

Thanks guys...i did realize the limitations with MAC/IP.

So, to give you a little bit more without divulging my business completely, the business i am launching will be almost like "One-person-one-vote" voting system. I don't think the app fails if people open multiple ids as i have other means of validating uniqueness of an account... but, i am trying to see how best i can identify users multiple accounts through other means(MAC/IP etc), and have a procedure of identifying, alerting users, and deleting their multiple (duplicate) accounts.

It's almost like i can open multiple accounts and vote for democrats, if i want to influence democrats to power. I am trying a voting platform that will enable each user to cast their vote - only once on an issue.

Any help in your suggestions from technology perspective would be highly appreciated?

idscore,

I think that on a diverse and distributed system like the Internet what you are proposing could be nearly impossible without physical authentication.

As has been said MAC/IP address isn't going to be the way forward even just due to people having access to multiple machines/public access/etc. before we even get into the realm of spoofing. Likewise multiple, unique individuals may try to access your system from the same IP or MAC address, a shared/public terminal for example.

As Shawal has suggested debit/credit card information should be unique, but a person can have more than one card legitimately (If I only had one my finances would look nicer )

Even going to the extreme of requiring physical authentication (such as RSA keyfobs, swipe cards, etc) whilst each device is unique, again an individual could have access to more than one device, for example registering/recieving one from multiple addresses.

However, whilst it may/will be impossible to get a 100% perfect system it is important to remember that you only need to remove enough flaws to make the system usuable. Holes can and will be found in any non-simple system, online or otherwise, what is required is reducing the level of holes to an acceptable level depending on your context and requirements.

Hope this helps, good luck

Just issue each person a digital key.   Use two factor authentication.