I use both hajur and tapain interchangeably but it'll depend on who I'm speaking to as well. For Eg: I use "hajur" to my parents, elders, relatives and in some cases, ladies (In ladies' cases, when they ask me something, I go "hajur?"). I reckon the usage of "hajur", "aisyo", "marji hos" et al is more widespread these days and is being used among people belonging to several different castes, not just a select few. 

There's nothing wrong with using these terms. More often than not, these terms are more pleasing than what I'd call "thado bolne". Before I get mistaken, there are quite a few people I know who refer to someone as close as their parents to as "garcha, khancha". For Eg: One of my buddies goes "Mero mummy le mitho pakauncha". And before I get mistaken, whilst his intent might not be to be rude, him saying "mero mummy le mitho pakaunuhuncha" or "pakaisincha" would sound much bettter, perhaps?