Why not just use Google Docs? It is free and works great.
Because:
1. You can only edit Google Spreadsheets and I believe you cannot create new ones.
2. You cannot edit documents and powerpoint files which documents 2 go can do.
3. For me Documents to Go was more powerful on my Treo than Google dogs was on my desktop.
4. Native apps are quicker than web apps.
5. I own a Google account as my trash email account. I feel uncomftable with Google and privacy and my job feels the same way.