Linchi Shea recently drew a couple of comparisons between Sybase ASE and SQL Server here. It's been a while since I worked with Sybase, but there were some features that it had that I wish SQL server had.
For instance, the ability to mirror files. In Sybase, I can have one logical file mirrored to two or more physical files. This allows me to be able to have a physical disk fail and the database keeps serving data. It also allows me to transparently move a database to new disk without having to take it offline. I'm sure that there are other features that both products can learn from each other on. File-level mirroring always impressed me, though.