[Frqy3]

From what I've seen, it is mostly Southerners (南方人) or Western people taught by Southerners who have trouble with distinguishing between endings such as -n and -ng.

Also, pinyin IMEs can be fairly fast even with only minimal practice as the matching is done at the word level (and possibly some IMEs look at preceeding characters) rather than at the character level. For example, when entering 南方人, my tying sequence was "nanfangren<space>", and the IME was already suggesting the correct answer at "r", so I could have actually typed "nanfangr<space>".

[andrezsanchez]

There are also a lot of phrases that can be typed with just the first letter from each word, eg typing "bth" gives "不太好", "zmy" gives "怎么样", and there are endless more combinations like this.

[mkristian]

"nfr" gives me "南方人"