How common is the use of "瞧" and which region?
As far as I know the people of Beijing and Hebei province often use 瞧,for example:

瞧病（go to hospital）
瞧您说的

In fact,In most north parts of China use 瞧，such as

让我瞧瞧（Let me see）

is often heard in Shanxi Province.
It is more often to hear such word in dialect than in mandarin.