Hawkbills: I like hawkbills; they work great for a wide variety of utility cutting.
Self-defense with hawkbills: Well, they're obviously good slashers. Depending on the point curvature, some can be quite effective stabbers (Emerson's version of Fred Perrin's La Griffe comes to mind, as does their P-SARK). If you want more detail on using these blades in combat, you might want to try posting in "Practical Tactical."
Sharpening hawksbills: They're difficult to sharpen with a bench-stone; not too hard with most of the "crock-stick" type sharpeners. Depends a lot on the amount of curve in the blade, and how dull the blade is.
Sharpening Serrations: Depends on the serrations, and on what you're using now. Most serrations are best sharpened with some sort of round or semi-round stick, like a Spyderco Profile. Cold Steel serrations are pretty much impossible to sharpen (though Lansky (I think) is now making a special tool designed to fit them). I have seen some serrations that are sharpenable in the same manner as a straight blade (stroking the blade along a stone). I think this is the style of Mad Dog's serrations, and I'm pretty sure I remember seeing this type on a higher-end United Cutlery Seal Team knife in ATS-34.