I'd say i synthesize 90% of my tracks. The only thing i don't synthesize are drum sounds. If you consider the MachineDrum to be a synth, then i guess that takes it to 95%.
For some reasons samples never cut it for me. I never manage to make them do what i want them to do.... I do like to use them for background atmosphere and eery drones though, as they often sound much richer than a synth patch.
I guess i'd give myself on a 3.5 out of 5 in synthesis. I worked a lot with very simple mono-synths, like the monoLancet or the SH-101, and learned more with slightly more complex synths like u-He Tyrell and more recently u-HE DIVA and the uWaveXT. Synthesis exploration is something i find much more interesting than mangling a sound with fxs and trying to pull out something of it. Somehow building a sound from scratch makes more sense to me.
Tyrell is a great freebie, and imo a great synth to learn more about synthesis on. It's basically been in all my tracks since the first alpha version was made public.