I consider it legendary because it's a never-before-seen pokemon, cannot evolve or be traded to other Pokemon games, and always a female which means it can't breed (or can it with a regular male Pichu?).
As far as I know, Heatran can't breed either (because it's always a male, therefore making it a legendary pokemon).
What do you think?

Source: http://www.serebii.net/heartgoldsoulsilver/pichu.shtml

In order for it to be a shiny pokemon, it would have to sparkle (like Pikachu-colored Pichu) when it gets released from its Poke Ball.

http://miragemaster.webs.com/pichupresent.png" width="126" height="95"> 

No, I don't think I would...

No, female means it can always breed. The mother's race is the one that comes out, right? Or have they flipped that rule?

Wait, I thought Pichu weren't capable of breeding at all.

Yeah, i had forgotten that. Baby-types can't breed, along with the one-shot legendaries.

get a ditto

According to what I've read, it traveled through time so it's possible...

Ditto is only the solution for male-only pokemon species (or if you happen to have a male you want to breed), not for types incapable of breeding period.

Pichu can't breed you perverts!

No, it isn't. One off and not being able to breed is not enough to classify as a legendary pokemon. If it were then that an obscene number of pokemon were legendary during Generation 1. Rotom is also one off, can't breed, has no gender, but is not a legendary. The classification is not set by a definition so much as a title assigned by the creators.