Many people have upghraded successfully.
If you've used Crystal Queries or dictionaries, you'll have to rewrite.
If you modified the SQL generated by Crystal, you'll have to rewrite.
Make copies of the reports, download the freebie version of CR XI (30 day trial), and test them, that's the only way to really know.
Basically if you bought into any of Crystal's proprietary BS, you're in trouble.
If you based reports on tables, views or SPs, you should be in fine shape.
I'm avoiding using Business Views/Universes for the same reason, eventually it'll probably backfire.
-k