I don't know if it's of use but I would like to revive this thread a bit.
I have been looking for similar solutions for a couple of days now and I find absolutely nothing...and I have not had the Google-only attitutde (which means, knowing about sync between iCal and Gcal for instance, that I looked up solutions with Excel, Numbers, iCal, FileMaker, etc.). But I would eventually need the same thing, which is a two-way sync between Gcal and Google Spreadsheet.
The only solutions I found (only for mac) are to export a carefully formatted Excel document in Ical and then, using Gcal sync with iCal, it would be imported in Google Calendar. This can be done with a little program called iCal Maker (http://www.mmisoftware.co.uk/pages/icalmaker.html)
But that means 1) exporting Google Spreadsheet as Excel 2) Format Excel doc to fit the requirements of iCal Maker 3) save as tab separated text document 4) process through iCal 5) sync iCal with Google Cal.
Not really the "sync" we all want...
The uses would be numerous, and most of all, I think that if going in that direction of integrating its apps, Google would make them a very good choice for collaborative project management. In my case, I need many people to collaborate to set the To Do's and their time scales in a Spreadsheet and then export that to Google Calendar, so that every person involved would be sent email/sms according to what they have to do.
Now, the API Java Class discussion given by Fozzy seems really on the spot, but this is only hinting at the fact that programmers can do this thing we need. Any idea if a gadget that would say "send to Google Cal" would be easily doable? And then, I was thinking of the 2-Way, because if another user changes an event from withing Google Cal, it would be pretty useful to keep the spreadsheet up-to-date...
Any idea about such features and such apps/gadgets?