I was one of those that "got rich fast" via glyphing. I was lucky enough to have an awesome friend who helped me a little with my initial investment, by giving me a few bank tabs worth of inscription materials to use my own brains to work with.
My strategy was to make 20 of each glyph that I knew, and restock when that stack dropped to 10. I started off only knowing the recipes you were taught from the trainers as I leveled my scribe up, but I sold all the glyphs I made. Once I reached cap level, I would just keep my supply up and craft a stack of each new glyph I learned from the cooldowns and books.
I had 3 bank toons for this. One was my main banker and only carried 3 classes in 32 slot scribe bags, so there was room for my odds and ends. I had two more toons devoted to glyphing alone, one with blue-spectrum, and one with red-spectrum classes. I did this, because it made it easy for me to visually see what glyphs needed to go where, and also whether I made a mistake and sent the wrong glyph to the wrong toon. Not that it's a big issue, but I have serious organization issues and inefficient use of storage drivers me bonkers.
I'd log into each toon in a rotation first thing. Postal would run and empty mail while I surfed forums and blogs, then QA3 would auto post everything for me. I had my threshold set to whatever would give me a 100% ROI depending on prices it was sometimes higher than 100%, and my fall back was set to 30g. When I finally rolled over to my main bank toon, after I posted up glyphs, I would then snatch up all herbs and inks within my price range, ship them over to my scribe and spend a goodly amount of time milling and restocking.
ProTip#1: Restock before the weekend. I would often make more sales over Friday-Sunday than I would during the rest of the week. Be sure to check in and make sure you're not incredibly low on anything.
ProTip#2: Empty your mail box, scan and repost as often as you can. The more posting I did, the more gold I made.
I might go into WHY this strategy another time, or else this post will be even more monstrous than it already is.
And then Blizzard fully announced the 4.0.1 changes. Glyphs are now a one-time-use-only item. Oh noes! The feelings over all were quite mixed, but I was one of those that knew the market would die down, but still survive. For two weeks prior to Glyphmas, I crafted my little heart out. I had a massive stock of inks and was scoring amazing deals on herbs (5g per stack!). I stocked 40 of each glyph, 60 of the ones I knew were very popular. I suddenly watched a small investment blossom into my first gold cap and beyond. I made over 180k within 4 days of that event.
And since 4.0.1, I haven't made a single glyph for profit. But the glyphs I'm still posting (only a small handful on one toon) are posting and selling for anywhere between 20g and 180g.
Tomorrow is likely 4.0.3a where more than a few interesting changes will occur to inscription and Azeroth as a whole. It seems the scribe vendors have fallen off their rockers and no longer sell or trade items relevant to level 80 and Wrath of the Lich King. Vanishing powder will no longer be purchasable from any vendor, but still craftable by scribes. Ink of the Sea will no longer be full currency for other inks, so seriously do your trading today if you intend to stay in the glyph market after patch.
My consideration is this:
I have two days to sort my crap out, mill my brains out, and then I can take it a bit slow. Or, I can just not bother, miss out on some gold from a rush of bored players leveling alts to check out the new Azeroth. Hmmm. Oh and don't forget glyph sales into Cataclysm. Hmm.
To glyph, or not to glyph?