You can really compress your timeline by running a TSQL_replay trace on your production server while it is in 80 mode and then replaying the trace results against your dev server while it is in 100 mode. Note of caution: running a trace on a production server can affect performance.
Replaying a trace will give you cycles against 100 mode with all SQL that is thrown at the production server, ad hoc or otherwise. Errors will shake out quick because it's a true workload...unlike the narrowly focused workloads typically seen on an instance used for development. There are some restrictions and running a trace in production should be done with a watchful eye but it can help you resolve the compat issues proactively, rather than passively waiting for them to crop up in dev.
http://msdn.microsoft.com/en-us/library/ms189604(v=SQL.105).aspx
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