As a developer, you will need to get an API key if you plan to push a lot more transactions once you have reached the limits. Without an API key, a rate limit of 5 requests/seconds is imposed so you may receive a HTTP 403 error if exceed this limit.
After registration, please create a FREE Api-Key Token from within the ClientPortal->MyApiKey area and use that with all your api requests. Either a link back or mention that your app is "Powered by Etherscan.io APIs" would be very much appreciated.
Note: The Ethereum Developer APIs are provided as a community service and without warranty, so please just use what you need and no more.