More details about the DSi were announced during the Game Developers Conference today, including the consoles downloadable content prices. The DSi Shop will allow you to download tons of games through your wireless connection, which will cost anywhere from 0 - 2000 points per game. The point-to-dollar system seems pretty standard (and perfectly reasonable) with 100 points costing one dollar.
There is some bad news coming for you Game Boy Advance fans with this new console roll out: your GBA cartridges will no longer work in the DSi like they did on the DS and DS Lite. However, to make up for it (and to encourage early adoption), Nintendo is tossing in a free 1000 points to all you gamers that pick up the DSi before October. That way, you can download your favorites so you don't go through GBA withdrawals. They are the classics, you know.