I learned formally that in the standard Beijing accent, zh, ch, and sh are pronounced more in the back in the mouth than j, q, and x. However, I got lazy and speak all six of these consonants in the front of my mouth. I'm curious, is this common for other speakers? Is there any region that speaks like this?
As you probably know it is very common to mix up zh、ch、sh and z、c、s.
Here they say that in many dialects zh、ch、sh can't be distinguished from j、q、x. But they don't mention which dialects.
On this page somebody says that Cantonese people can't distinguish the 3 groups of consonants in j,q,x,zh,ch,sh,z,c,s
On the same page they also write that the consonants jqx are pronounced as /zi/,/ci/,/si/ in Nanijng.
In the Chaoyang dialect there also seem to be such mix-ups. But not for all words. For example x、sh are read as j、q、zh、ch, for example in 喜(～鹊)、跹(翩～起舞)、械(机～化)、摔(～跟头)、尚(和～)、殊(特～)、匙(钥～)、始(开～)
j、q、x and z、c、s are often mixed-up. For example in: 俗(风～)、宿(～舍、住～)、狙(～击)、沮(～丧)、咀(～嚼)、俊(长得～)、峻(险～)、竣(～工)、骏(～马)、(～包)等。
In Northern China they should never be mixed, unless you are a Japanese tourist. j, q, x, has no equivalence in English, so you have to learn it. However, for Cantonese speakers attempting to speak Mandarin, they might get hopelessly mixed and others allow for that.