You're basically right though, there are regular calls on /r/bitcoin for people to run a full node because the number has gone down recently. I decided set one up on my dedicated host due to one of these.
Interesting - I have been meaning to look into how the blockchain works (I missed the get-rich-quick rush and dismissed it all until heard Andreessen explain the reasons)
Simply run bitcoin-qt or bitcoind all the time and make sure that you have port 8333 open to the outside world (if you have a router, this usually means forwarding 8333).
It takes a few hours to a half day for the node to catch up, depending on your bandwidth and CPU, but after that it requires relatively little processing time. But you do need ~20 GB of free hard drive space for the blockchain.
