Got a Google Spreadsheet test account and decided to take the web app for a quick spin.
The spreadsheet as you can see above behaves as a normal desktop spreedsheet should - so much so, you will be forgiven for thinking you were using a desktop app. The spreadsheet does things such as error checking in real time (as seen below when I put some garbage into the formula)
Can it load from an Excel spreadsheet?
I quickly put together an Excel spreadsheet and upload it to GoogleSpreadsheet
It works!, and it keeps the text formating from Excel along with the formulas and I didn't even have to convert it to CSV.
A strange thing I found though was it only loaded the columns and rows that had data in them if you needed to add more you have to use the insert menu and choose if you wanted to include a column or a row.
Oh well those were simple tests, but so far it seems to do the business. Will see what happens when I throw some more complex things at it later..