We had our first 3PAR 2009, second 2010. Both have now disappeared into the recycle bin so may still be running somewhere.
Since then we've had no downtime for;
Software updates (major and minor versions)
Additional Nodes
Additional Cages, including Moving Disks
Additional Disks
Additional Cards
Moving volumes between Disk types and Raid types
Replacing Disks, Cards, Nodes, Memory, Cables etc
Unsurprisingly we have had downtime for (but services were moved live to other arrays to reduce impact);
Moving arrays between buildings/rooms
Turning power off to buildings
So generally speaking tis good stuff.