While it should technically be -ku arimasen, it's actually rarely used, and -kunai desu is more "mainstream".

> Past tense is "suki datta". To make it polite "suki deshita". Negation is "suki de wa nai" (seriously, romaji makes me cringe...). Polite negation is "suki de wa arimasen"

Trivia: all these forms are really variations of "suki de aru". "datta" comes from "de atta", "de ha nai" is really "de nai" with a "ha" for emphasis. "de ha arimasen" is really "de aru", with the "ha" for emphasis, and "aru" conjugated with the "masu" auxiliary at the negative form.

> Very obscure piece of trivia (that most Japanese people don't even know) is that "ohayou gozaimasu" is actually one of those conjugations -- it's actually "(honourific) o hayai de gozaru" in polite form. The "i" ending mixes with "de" to produce the "ou" ending.

Technically speaking, the -i and the de are not combining at all. The -u form (ウ音便) comes from the -ku form (連用形), where the k is removed. Then the preceding sound also changes (like in arigataku -> arigatou ; oishiku -> oishuu, etc.). The typical forms used in keigo are -u gozaimasu and -u zonjimasu (where there is no "de" to combine in the latter ;) )

I think the Japanese learn the ウ音便 in 国語 or 古文, so I don't think it's some obscure trivia that few people know. In fact, you can hear it in e.g. 時代劇 dramas.

Also, the form is pretty common in Kansai dialect (without gozaimasu). In fact, wikipedia claims[1] it comes from there and the gozaimasu was added in Kantou.

1. https://ja.wikipedia.org/wiki/%E9%9F%B3%E4%BE%BF#.E5.BD.A2.E...