-i adjectives

[Diggity]

Ok just wondering how I should learn these adjectives. I am just starting chapter 5 of the Genki book. The Genki book tells me to conjugate them like this :
Omoshiroi

Present : Omoshiroi desu
Pres Neg: Omoshiroku arimasen
Past: Omoshirokatta desu
Past Neg: Omoshiroku arimasendeshita

I know that this is probably "proper" Japanese. I know that this site has different endings for the adjectives and are probably "spoken" japanese. Is it worth me learning what the textbook has first, then after this chapter is over replacing it with what is on the site?

[Mukade]

The form you've posted here is, as you've suspected, proper, polite Japanese.

I'd say that if you only know one form in Japanese, it should be the simple polite form (often called ます-Form in textbooks). You don't want to be speaking in casual forms to your teacher or your boss or your friend's parents as it is quite rude.

Once you've picked up that simple polite form, you can start focusing on more casual, conversational forms.

[Diggity]

Well in the textbook it gives a footnote saying that:

"Some speakers follow a more regular conjugation, where desu is inert in both polarities (affirmative and negative.) For these speakers the chart loos like the following :

affrimative negative

present ~idesu ~kunai desu
past ~katta desu ~kunakatta desu"

Ok, so I guess my question is, does this footnote just make me aware of what Clay has on his grammar page about this, or does it mean that this is an acceptable way of conjugating adjectives with anyone you talk to?