For the solarwinds.com site I often refer back to the documentation section and the price page every second week or so. I'll also grab new product evaluation versions for labs and training.
The customer portal is used to obtain and manage licensing for various clients. Time interval for this varies depending on assigned projects.
I joined thwack before becoming a customer. This was primarily for research and reading up on the SolarWinds modules. I try and visit thwack as often as I can to keep up on releases and to see issues other users are having. If I'm having an issue with a particular customer request or general question, I find thwack is better than support (I reserve support for "this is broken"). Thwack is also a great resource for NCM device templates and SAM templates.
If I get some downtime at work, I usually come to thwack to browse the latest posts (although the "Recent Content" only allows you to hit More a few times so I usually get a limited amount of recent stuff). It would be nice to be able to filter out people voting/rating and just see posts though. Sometimes it's easier to just open up tabs for all the different sections I'm interested in and look at the recent threads that way.