Personally I'd say no.
It really depends on how tied you are to Oracle's features and whether you are simply using it as a datastore and not using the more advanced features.
MySQL 5.0 does support procedures, triggers etc but with all due respect they don't match up to Oracle's implementation at the moment. For example there is no support for packages and I know in the past there have been instances where I have used Oracle packages which could not be replicated in MySQL without major updates to the application (I'm thinking of overloading for example). There isn't an equivalent to UTL_FILE or DBMS_OUTPUT which are two areas which are used a lot in Oracle procedures.
There is currently no job scheduling facility in MySQL, no support for sending email (a la UTL_SMTP), no materialized views and any number of other things Oracle does.
I'm not trying to say Oracle is better than MySQL, what I'm saying is if you have used Oracle to it's full potential over and above it's database functionality you might need to look outside of MySQL for the answer to many of the things you have implemented.
As a database, no problem, with the extended features it's going to be hard.
Andrew Gilfrin
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http://gilfster.blogspot.com
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http://www.mysqldevelopment.com
MySQL Stored Procedure,Trigger, View.... (Just about most things these days) Information