I've used Google Docs Presentation before as well and it works pretty well, especially if you're creating a shared presentation between users in different places. It's a lot easier to create it there, even if you plan to use MS PPT for the final presentation since you can capture revisions and export it into PPT format from Google.
There are some differences that may be available but I haven't been able to figure them out yet, like how to write notes to correspond with slides in Google. In a regular PPT, you can write notes to yourself for each slide that are not visible externally. I had to create a separate Google doc to share notes for one we created in Presentation. I've also not tried to do any animation or timing within Google Presentation so I don't know if those are similar functions or not.
Hope it helps!