I load up if I can, so I don't feel guilty about using it. Streaky Sapphire, Lemongrass, Sandstone, Bubblegum Pink - anything that wasn't in the regular line that I use a lot of. Sometimes it sells out and I planned ahead, sometimes I just have a lot of glass that other people have, too.
Until it's completely unavailable, like Vetro dark ivory. I have 12 lbs (holy crap that's a lot) of it and wince when I use a rod.
Sometimes I remember Sheryll's sound advice - "It's paid for, use it!" and melt with wild abandon, but it's rare.