Yes it seems you find the offers by being specific about the currency, specific as in who issues it. For example the WeExchange gateway deals in bitcoins, USD, CAD and Australian money so those are the most well known currencies so far probably. So you'd put their bitcoin-denominated account's number as issuer for bitcoins to see offers to deal in their bitcoin IOUs, their USD denominated account's number as issuer of USD to find offers to trade their USD IOUs and so on.
I do not know why they use a separate account for each type of currency, I am so far using one test account for all currencies, it is rpVft3wic2fZ2saY5BjEtL8R2NPrubxWG5
Because I run the Digitalis Open Transactions server I already have issued a lot of assets there, and am looking to issue a bunch on Ripple too. But I cannot do many offers yet until I get more ripples as most of my ripples got spent on testing the trading system to learn this much.
I have quite a bit of Devcoin (DVC) and Groupcoin (GRP), less (twenty thousand or less) I0coin (IOC, as Ripple currencies are alpha only not alphanumeric) and Ixcoin (IXC), very few Namecoin (NMC) and Coiledcoin (CLC). Other "altcoins" I have too few so far to get into market-making with them. I also have a slowly growing number of BBQcoins (BBQ).
Basically you should be able to type in pairs like BTC/DVC, if issuer of the BTC is not shown was weex then change issuer to weex; for DVC likely it will default to your own account as issuer, or if you already trust someone for DVC then their account; change issuer to my account shown above and if I have managed to place any DVC/BTC offers, or if anyone else makes any offers involving my DVC IOUs, you should see them.
SO far because the client only shows five decimals of price I only have an offer to sell DVC for 0.00002 BTC each, which is way higher even thatn the 200 or so satoshis they used to go for a couple of weeks ago. We need more decimals in the client to display reasonable "bitcoins per devcoin" prices.