Online Backup vs. Tape Backup?

hashbox asks: "I work for a small non-profit (about 100 staff members) and management has decided that they want to use an online data backup system instead of our existing tape backup system. After a meeting with one of the many vendors providing this service, I must admit that I am impressed with the promise of the technology (ease of use etc). However the sysadmin side of me has a few reservations. Has anyone here on Slashdot used an online backup service, and what were your experiences?"