Writely and Google Spreadsheets are fast becoming a regular part of my mobile life, and now here’s Slideshare jumping into the mix. (TechCrunch this morning turned me on to it.)

Slideshare is a bit different from some of the other “Office-killer” apps popping up across the Web (and ZohoShow and Thumbstacks are also players). Rather than Being a direct assault on Word and Excel, these PowerPoint sharing tools are more what YouTube is to a video editing app: the next step in the process. After you’ve done the heavy lifting and created a presentation, they let you share it without having to send a bunch of thick e-mails around.

These services sound cool, aside from the fact that it’s hard to imagine a sustainable business model for any of them (especially because Google is all but certain to buy one and offer it up for free). So maybe Google buys one, if it’s not developing the same thing in-house, or maybe Microsoft even buys one, if it isn’t already building all of the features into its Office Live strategy.

But either way, I’m guessing it’s one of those situations where Pandora’s box is open, which is good news for the mobile worker. These services are likely to get more secure and feature-rich, to the point where we’ll have access from all sorts of places and devices.