Always the same deposit address for a user?
The bc.info receive paments API will NOT work if you reuse addresses. The funds will still be yours since the addresses are hierarchical deterministic, but the callback notification will not fire. Your site will not know when a new deposit has been made unless you check manually. I suppose you could create a "refresh my balance" button for your users, but you'd need to put some restrictions on how often they can click so you don't exceed API request limits.