If you are using the latest Nice Memberships version 1.11 (or greater) for Joomla 1.6-2.5, your service will not be effected. The 1.11 version contains the new HTTP 1.1 requirement to communicate with PayPal's IPN system. All other versions of Nice Memberships will need to be upgraded, by February 2013, to avoid interruption in PayPal's IPN service.
The easy solution is to download the latest version of the Nice Memberships extension. And simply re-install it. However, no doubt that, some of you will want to manually patch the extension's scripts yourself. This article will provide you with a step by step for applying the code changes.