Ethereum addresses are displayed in HEX, so they are not case sensitive. You could capitalize or lower-case any of the letters, and the address is still the same since A and a are the same in HEX.
However, our wallet does a checksum to see if the address is valid, and the capitalization is used to make this check. When you send it though, this transaction will still go through and show up just fine.
When in doubt, always send something small first to make sure, but in the case of capitalization, it won’t make a difference.
Please be aware that this is valid only for Ethereum addresses. In the case of a Bitcoin address, it is important to stay with the exact format that the address has (with exact capitalize and lower-case letters).