I was excited about the e-Reader add-on for the GBA when it first came out, because it had a ton of potential. It still does, but it's barely been used by Nintendo themselves (Clu Clu Land or Urban Champion are not what I'd call system-sellers), and not a single third-party developer (AFAIK) has taken advantage of it yet. Apart from the freebie Air Hockey card, it's been a waste so far.
Apparently not for long.
NES Super Mario Bros. 3 is coming out for the GBA in September as Super Mario Advance 4... and the following speaks for itself:
Nintendo's planning on releasing a series of e-Reader cards for Super Mario Advance 4 where players can transfer the data from e-Reader to the game (much like the way Pokemon Ruby/Sapphire handle the special Battle Card-e fights) to upload brand new levels and challenges. You'll need two GBAs (or a Game Boy player and a GBA) to take advantage of this feature.
SMB3 with new levels? Do I hear cash registers ringing?
EDIT: Oh yeah -- I've now played WarioWare, Inc. I may never sleep again...
(edited by vsp on 4.7.03 1557) "You may be wondering why I have been making so many references lately to Fox News. The reason is that it is now my cable news network of choice -- because if I’m going to watch the news and be lied to, I want it to be ridiculously obvious that I am being lied to." -- Center for an Informed America, Newsletter #34