Against bosses, I like throwing arcane blast in there every 8 seconds as best as I can control it to get the cheap 195 mana shot and lengthen my mana. This applies especially against BG bosses.
On the other hand, in Shatthek Halls once, arcane blast saved my group because I started chain casting it on the first boss after it seemed I would have enough mana to take him all the way down. Our main tank died and then our warlock was tanking for a while (I hate warlocks, I realy do, but somehow this tank was working as a delay tactic). Our other mage stayed around long enough to deal some damage and then delayed slightly longer for the few hits he lasted and the birdman started coming towards me, but arcane blast had generated enough damage that just as I ran OOM and the boss was incoming, he dropped. I don't think frostbolt would've caused enough damage to take him down.