It really depends on the type of business. Notably, a lot of smaller direct sales web companies have almost all of their traffic come from SEO.
Most sites I have been involved with see 50%-70% of traffic from search. More brand equity = less importance for search.
More importantly though, search tends to convert way way better than really anything else (ppc included) when goals tracking (ie nav to contact page and thank you page).
You can probably give your traffic a lot of growth by investing more time into efforts with SEO in mind. Let me know if you need help. :)