Glyphs will also be saved with your 2 different specs. So different glyphs for the 2 different spec. So only will have to buy glyphs once for each spec.
"Nethaera: Will you be able to change your Glyphs as well? Ghostcrawler: Glyphs will be tied to each talent spec so that if you switch between them, so too will the Glyphs. You’ll notice the UI will have changed a little bit so that the Glyph panes show up alongside the Talent panes now that they are associated. " http://www.worldofwarcraft.com/info/underdev/dualspec.html