Lilac is the greatest self bow wood I've laid my hands on. Crowned-back stick selfies safely pulling 60#, 1 1/8" limb width and sub-1" set (no heat-treating) count as great in my book.
From what I've heard, lilac should be even stronger south from the cold, dark north where I live.
Lilac grown on open ground (*like in Dana's pic) is almost always twisted beyond use. Bow lilacs grow in dense, "overgrown" habitats where they have no time to get all twisted and gnarly when competing for light and survival. Lilac growing on moist, rich soil is better in ring quality, too, compared to the thin-ringed, lighter-wood lilac found on dry, windy spots & poor soil.
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Tuukka