If I purchase a card (or similar device) that claims to mine Bitcoins at 10 GH/s, will that device also work for other currencies? That is, would the device also work on a multi-pool for litecoins, dogecoins, etc?
ASICs (Application-specific integrated circuits) are especially manufactured for one specific hashing algorithm. Therefore, a Bitcoin ASIC using SHA-256 will not work for Litecoin or Dogecoin as they both use Scrypt. One example for ASICs are the Butterfly bitcoin miners.
There are altcoins that also use SHA-256, such as Freicoin, Peercoin or Namecoin. An overview can be found at altcoins.com.
CPU and GPU can be used for any Coin, but the number of hashes will be different. A card mining SHA-256 (Bitcoin) at 10GH/s will produce much fewer hashes in Scrypt (Litecoin, Dogecoin), because Scrypt is much more complex.
It really depends on which kind of card. If it's a GPU you can mine whatever you want. If its an FPGA which you can reprogram you can switch to the scrypt algorithm too. If you purchase an ASICS (i.e. butterflylabs) this means it's optimized to work with SHA-256 algorithm only and will therefore not work for "scrypt-coins" (dodge, ltc, ...).
Now that I think of it, since Quarkcoin applies several different hash functions in series, and one of them is precisely good-old SHA-256, you could theoretically use that box to speed-up quarkcoin mining by changing the miner software to take advantage of the ASIC's hash power just for that small step, then take the result back to the CPU for further processing.
It'd require significant changes to the miner, of course, and I don't think gains of more than 15% could be seen - and probably that number's too optimistic.
So besides freicoin, tigercoin and others that use pure SHA-256 as their proof-of-work, here's another coin whose mining could potentially benefit from a spicy Jalapeño.