Consider the following line, which I've heard this particular construction frequently:
"I’m curious if other people feel like I do."
The construct specifically is that of using "I'm curious if" to preface something that the speaker is curious about.
I was recently told by someone that this is improper English, as it implies a conditional - that is, "If other people feel like I do, then I am curious". The proper way suggested was "I'm curious as to whether other people feel like I do."
I can see where it's coming from, at least that the former can be read in that fashion and that the latter is unambiguous. However, is it actually improper or logically incorrect?
Prior to asking this question, I did a quick check on this site - there were at the time 48 instances where users used the phrase "I am curious if (some situation is true)", while there were 46 instances where users used the phrase "I am curious as to (whether something is true, where the rule works in this fashion, etc.)". So they both look equally used, and the users using them ranged from new users to reaching the 20k reputation level, so it struck me as not something about being improper English. Rather, it struck that if anything it might be considered maybe a colloquialism or otherwise casual lingo.