It’s actually barely usable for any serious kind of work (which is where most of the cash in Excel cash cow comes from):

• No autofill – I unsuccessfully tried to drag a range (1, 2, 3 for example) down to fill out, say, 20-30 consecutive numbers. No luck. Ctrl-D/Ctrl-R shortcuts for copying right/down do work though.
• No charts – Much less important than other things I’ve mentioned, but still a significant omission (Excel charts are not perfect by any measure though)
• No offline access – One of great points mentioned by Ian Landsman

In my humble opinion, this is a case of just too much blogosphere hype with little real substance.

Update: iRows seems to be more useful, though less sleek than Google Spreadsheets: autofill, charts are included. And it supports collaborative editing to boot.

Although it’s well known that most of the time Excel is used for fairly basic tasks, most of the biggest users (consulting, corporate finance, investment banking) use a very wide subset of functions including:

• External database queries
• PivotTables (extremely important)
• Large, complex spreadsheets (30+ sheets in a single workbook)

Which Google Spreadsheets is unlikely to offer in the short term (although I’m willing to be proven wrong). Most importantly, data that ends up in the spreadsheets is of confidential and/or proprietary nature and wouldn’t be on an online service.

That doesn’t mean that Google Spreadsheets won’t have its users, it’s just not a threat to most of the core Excel customers.