The creative folks at CommonCraft.com have come up with a great explanation of the benefits of using web based document systems like Google Docs, Spreadsheets, and (as of today) Presentations.

They've focused on the collaborative benefit. While Google Docs are seriously underpowered compared to their Microsoft counterparts, being able to easily collaborate on a secure shared document is worth understanding:

However, there are other reasons one may prefer using web based documents. Data backup is a huge one worth considering. When is the last time you backed up your computer. I bet Google has a better backup routine than you have in place.

Web friendliness is another concern. Documents drafted as Google Docs repurpose as blog posts very easily since the formatting is done in HTML. Copy/paste the HTML from your Google Doc into your blog program for a nicely formatted and spelled checked post.

Speaking of spell checking, I imagine Google could learn new terms on the fly and continually improve their spell checker, unlike client software that would have to be updated with new terms.

Looking at Google's current suite of web based Office style programs, I'd rank their importance:

1. Docs
2. Presentation
3. Spreadsheet

While Docs will be used the most, the benefits gained from collaborative Presentation building makes it a very close second for me. I can't remember a time when someone I know created a PowerPoint alone. It just doesn't happen. They represent the work of groups, so allowing each member to fact check and improve the content relevant to them should lead to faster creating of better presentations.