Securing the information Transmission over the internet is most important for any organisation.
For SAP Portal we generally follow
1. web dispatcher
2. Reverse Proxy.
along with the SSL (https) Protocol.
what i have seen is generally First we do http only and go Live with Reverse proxy such as Apache .Then we plan for https.
But my suggestion would be plan for https along with Reverse proxy in the first place if you are planning to make your site available on internet.
Recently i had come across a situation where we faced issue while enabling https on a already running portal without reverse proxy.
internet explorer would display page not found error for the portal.I had asked a question on sdn but got no answer.
when we searched for sap notes, we came across SAP Note : 1663313 SSL not working after applying Microsoft KB 2618444/2585542.
After applying the note it started working.
Important observation is if your portal is patched approximately to the latest release or you are having a reverse proxy in front of portal then you will not face this issue.
Hope people will find this useful.