Beware of any 4GB SD card that you purchase through E-Bay. There are many sellers that are selling 1GB cards as 4GB. They do this by reprogramming the 1GB card so that the computer thinks that it is a 4GB card even though it only has a 1GB flash chip in it. Then they lable it as 4GB and sell it to you.
Over the last 6 months I have purchased three Samsung 4GB Mini SD cards and one 4GB OEM SD card from three different E-Bay vendors. All of which would worked fine until I tried to copy over 1GB of data onto them. Once you reach the limit of the chip inside, writing more data corrupts the chip and destroys the card so that it is no longer usable - you cannot even reformat the card because the flash chip is corrupted and probably will not show up as a removable drive on your computer. If it still shows up, it will say that it is unformatted, but you won't be able to format it.
After the fourth card I purchased had this same problem, I became suspicious that the problem was not my computers or card readers. So I decided to open up the cards. By looking up the part numbers from the actual Flash chips inside, I discovered that ALL of the cards had only 1GB of Flash RAM. This is obvoiusly a widespread scam on E-Bay as none of the four cards I purchased were legitimate. Fortunately, there is an easy way to test for this fraud. Before you leave feedback, make sure that you test the card by filling it to the advertised 4GB capacity. If the full 4GB copies, you probably have a good card. If the copy crashes and the card gets corrupted so that it is no longer usable, you probably have been taken.
Usually, the seller is willing to take the card back for exchange or refund (minus the shipping). However, the card that they exchange will probably do the same thing and the shipping charges are usually high. They may also try to convince you that the problem is with your hardware. This worked to delay me from finding out what the real problem was until it was too late for me to do anything about it. Hopefully, this won't happen to you.