From the OP, I keyed on the annoyance of having the crackberry go off all day long with these types of messages. Why not setup another email address which you hand out to your Uncle and other family members or friends who do this sort of thing and then not setup this address on your phone? You're then in control of when you respond to these messages and can deal with them appropriately.
I'm a big believe in setting up email rules so you could set some up based on the sender or even keywords so you can choose to ignore as much as possible and easily scan the messages they send for something with a subject which looks "important" or original instead of forwarded.
I'm sure there are also a number of sites which have "email etiquette" postings which you could forward on as a hint.
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