I've recently signed up for Google Apps, based largely on an article on Lifehacker. One interesting point was the idea of using a catch-all email address to block spam, as described in a comment or with somewhat more detail in a different article. Both explanations omit a relatively minor point that can lead to some frustration.
To summarize the method, you just set up filters in a catch-all address to identify email that matches a simple pattern, and forward it to your own account. The result is that you can give out email address "aliases" for, e.g., web registration forms, without inviting spam to your real address. If you start getting spam to one of the aliases, you can block it directly with a filter.
I set this up, and sent a test message to try it out. The message showed up in the catch-all account, but didn't get forwarded to my own account. The filter I used to set up the forward was identifying the messages correctly, but didn't send it on for some reason.
After a fair amount of web searching, I found the answer. Email for Google Apps is Gmail. Gmail does some modestly smart things to present a convenient interface; perhaps the best known is the way Gmail groups messages into "conversations." Something else it does is to hide messages that you've forwarded to yourself. This seems quite sensible in the context of conversations.
It's probably clear what was happening, at this point. I sent some test messages from my own account, which was then forwarded back to me from the catch-all account. Gmail sees a messages forwarded to myself, and doesn't show it. I'm left scratching my head in puzzlement.
After finding out about the hiding of self-forwards, I try sending a test message from a different account. It forwards without any trouble. Thus, for testing, you should always use a different account to send email than the account you want to receive it in.