Wow. It's a lot better than Google Spreadsheets. It's kind of sad that big companies applications get users and publicity, while better products from small companies goes unnoticed.
iRows appears to work better on Firefox on Ubuntu Linux (Edgy). Google spreadsheets seems to be pretty kludgy on Linux/Firefox.
So Google Spreadsheets is indeed a "killer app".
Read this post from iRows blog (June):
[I updated the post with a statement from Google.]