Google spreadsheets are now available from labs.google.com as a limited test. What I have seen so far suggests that Microsoft will not be too happy but those of us in the majority who don't need a full blow package such as Excel will love the Google Spreadsheets initiative. If you have ever used a spreadsheet before then the Google interface will not faze you one bit. It has been really well thought out - almost to the point where I was forgetting that this is an online application (you can't do right button clicks and expect to get cell options - you get the browser options of course!). When you save a spreadsheet it is stored on your Google account so its accessible from anywhere and you can invite other people to view it and chat to them (apparently). It is no where near as comprehensive as Excel and personally I would not want it to be. If I need a hugely functional app I will purchase Excel or something better but what is actually available these days? I am not sure - could even be that Excel uptake has killed all spreadsheet competition.
This is a cracking move by Google and if they follow up soon with an online slide show/presentation application then they may well not get a Christmas card from Redmond this year.