Practically anyone that types Japanese on a computer uses an IME to type the pronunciation in kana (latin letters or kana directly) and then converts words to kanji. I don't like having to pause and constantly check the conversion when I write. It slows me down and is plain annoying. So, I searched around and found there have been a few attempts to develop a way to input Japanese directly.
I found three different systems: NIK-code, T-code and TUT-code. NIK-code is based on the idea of type kanji by their components like when writing by hand (each component is assigned to a key). T-code and TUT-code is based on the idea of inputting a kanji by only pressing two keys (allowing 1600 combinations, more by extending to three keys).
I have slowly learning T-code for over a month and loves it. Here is some differences I have noticed between using an IME and T-code.
Learning effort
Learning to input kanji by typing their sound with latin characters require little effort beyond memorizing the conversion chart for the kana. Possible problems comes if you have to use a keyboard layout you are not used to.
Typing kana directly and then converting kanji requires memorizing the kana keyboard layout, but nothing more.
T-code requires a lot of memorizing, since the key combination for producing a character is entirely based on its frequency.
Speed
Since inputting by sound requires conversion for producing kanji, you must stop now and then to trigger it. Other issues that slows down input is if the suggested kanji is not the wanted or that the IME have defined the word boundaries wrong.
With direct input the typing speed is only dependent on your typing speed and how well you know the key combinations.
Touch typing (aka Blind typing)
It is theoretically possible to touch typing with an IME, but it requires a lot more memorization. You must know not only the pronunciation of a word, but also were it is placed in the list by default (must disable reordering by how frequent you type a word).
Touch typing with T-code is essentially no different from learning to touch type a language like English. The main obstacle is to produce characters that are not included in T-code, but that can be solved by extending with three key combinations.
Links
Home page for TUT-code (Japanese)
T-code home page (Japanese)
Brief description of T-code (English)
A lazy man's guide to easy typing (Parts 4-5 are about Japanese, English)
I found three different systems: NIK-code, T-code and TUT-code. NIK-code is based on the idea of type kanji by their components like when writing by hand (each component is assigned to a key). T-code and TUT-code is based on the idea of inputting a kanji by only pressing two keys (allowing 1600 combinations, more by extending to three keys).
I have slowly learning T-code for over a month and loves it. Here is some differences I have noticed between using an IME and T-code.
Learning effort
Learning to input kanji by typing their sound with latin characters require little effort beyond memorizing the conversion chart for the kana. Possible problems comes if you have to use a keyboard layout you are not used to.
Typing kana directly and then converting kanji requires memorizing the kana keyboard layout, but nothing more.
T-code requires a lot of memorizing, since the key combination for producing a character is entirely based on its frequency.
Speed
Since inputting by sound requires conversion for producing kanji, you must stop now and then to trigger it. Other issues that slows down input is if the suggested kanji is not the wanted or that the IME have defined the word boundaries wrong.
With direct input the typing speed is only dependent on your typing speed and how well you know the key combinations.
Touch typing (aka Blind typing)
It is theoretically possible to touch typing with an IME, but it requires a lot more memorization. You must know not only the pronunciation of a word, but also were it is placed in the list by default (must disable reordering by how frequent you type a word).
Touch typing with T-code is essentially no different from learning to touch type a language like English. The main obstacle is to produce characters that are not included in T-code, but that can be solved by extending with three key combinations.
Links
Home page for TUT-code (Japanese)
T-code home page (Japanese)
Brief description of T-code (English)
A lazy man's guide to easy typing (Parts 4-5 are about Japanese, English)

I'm just telling you what I see every day at work. Also if I ever need to use the shared computer, it's always set to direct input.