I'm a self-declared champion of free software and I use it whenever I can. My office suite of choice is LibreOffice and it does everything I need. Mostly, this is just presentations, so I was excited to discover that newer versions (4.0.3+, I believe) support the use of your Android phone as a remote control for your Impress presentations. A rough guide is on The Document Foundation's site but here's what I did to get it working on two Ubuntu 12.04 laptops.
First, you need to establish a Bluetooth connection between your laptop and phone. I had to check if my laptop(s) actually had Bluetooth. It turns out they don't but I have a basic Bluetooth dongle (seriously, who chose that word?) that I used on my old desktop for years. When I plugged it in, Linux detected it straight away and the Bluetooth icon appeared in my system tray. From there, I activated Bluetooth on my phone and made it discoverable, before using the computer to establish a connection. The computer provided a PIN number that, when prompted, I entered into the phone.
Now, the process wasn't seamless. I tried several times and needed to "forget" the computer at each new try. But eventually it got through. The only nagging issue was that both computers turned up as ubuntu-0, which totally confused the phone for a while.
Meanwhile, you need to enable the remote control in Impress. Dead easy. Open Impress, select Options at the bottom of the Tools menu. Then, expand the Impress tab and select General. There you should see the option "enable remote control", which you should check. Then you need to fully restart LibreOffice by closing everything. Basically, when you start LibreOffice again, you must see the splash screen. Now you can open your presentation in Impress.
On your phone, you obviously need to download the remote control app. With that done and the Bluetooth connection established, open your presentation you should find the computer listed on the screen. If you select it, it'll say "no presentation running" and give you the option to start it, or cut straight to the presentation.
There are a few things I didn't find obvious, so I'll share them here, now. First, the up and down volume control correspond to the right and left arrow keys on the keyboard. If you have animations in your presentation, they're the only way I know to make them work. Second, you can press the clock to choose between the time, a stopwatch and a countdown timer.
The app is quite nifty but I'm not sure how useful it is on a small screen like my Nexus One. I'll probably end up sticking to presenter mode but it might be a totally different story on a tablet.