I agree that in informal speech all relative pronouns can be, and usually are, dropped by native speakers, unless they are followed by a verb:e.g. "The man who gave you the money is my brother" (cannot be omitted).
However, it is often necessary to insert a later preposition to balance the grammar, e.g.
"The bank where you invest your money has gone bankrupt"
-> "The bank you invest your money in has gone bankrupt"
"I can �t remember the name of the garage where we had the car repaired"
-> "I can �t remember the name of the garage we had the car repaired at"
I think some confusion often arises when we look at written English, which is often slightly more formal and correct, to try to deduce spoken English where the grammar rules are treated much more flexibly by the majority of speakers. The boundaries of what is acceptable are always being pushed too and as English is not regulated by any official institution it will constantly evolve. It �s what makes it such an interesting - and often infuriating - language to teach!
