> Starting your posts off with a brief introduction of who you are is often a good idea.
IF most of your readers don't know what you are doing. I think this was written for their community (not HN), so most of them know what Flattr is about.
Also, they have "About Flattr" in the footer - not very prominently placed, but still find-able.
It isn't just Flattr: I encounter this issue regularly when being linked to startup blogs. Having one sentence or one link on every page that succinctly describes what you do just seems like a good idea. The web is made for linking, and not everybody will walk through the front door.
IF most of your readers don't know what you are doing. I think this was written for their community (not HN), so most of them know what Flattr is about.
Also, they have "About Flattr" in the footer - not very prominently placed, but still find-able.