Don't have my license yet, but for me it's definitely building homebrew (i.e. designed by me) transceivers. Not actually that interested in talking to other hams except for then testing my gear.
Heh, I'm not that interested in talking, but I am interested in typing. Especially with the advantage of advanced math/error correction, store and forward, relaying, and related. This adds up to a few watts in a $100 radio getting across a country.
Not sure if you mean building or designing and building. But QRP labs has some nice kits.