Boots up fast, everything is ultra responsive - compared to windows xp on the other side of the laptop.
Lotus notes on wine works surprisingly ok. ( damn you IBM for lotus notes )
Cisco VPN !!
Java compilation time - 20% less time than windows
Multi desktops, desktop spanning.
Wireless support much better from Dapper onwards.
Hard drive never starts threading - uses virtual memory the way it is supposed to be.
I run lot of stuff all the time and the OS never twitches.
Lotus notes ( damn damn you IBM )
Colibri - perhaps there is an equivalent - havent researched
Lot to catch up with OS X - but far ahead than that thing called windows.