I have a confession to make. Whilst procrastinating (I'm supposed to be writing my journal paper), I have been geeking my brains out. Mainly just for the purposes of being difficult, I use Linux for pretty much everything, and I have gradually been moving the things that I regularly do to Linux clients.
We use an Microsoft exchange server at the lab for handling mail; however, contrary to all expectations, there are superb clients out there that can happily handle the bizarro communications needed to handle mail on it. However, to be difficult, I insist on using creaky and ancient text-based pine for reading and writing email. That's right, folks, old school text based email.
Pine is great because you can get right in there and muck about with the headers of the email before you send message; surprisingly enough it's not too hard to get it to connect to exchange, and since it works in a text window it works wonderfully when your available bandwidth is choked with other stuff. Even though its under a proprietary license, for working purposes, its free (as in beer) to use.
The user-base for pine is still large and active, and there are plenty of resources out there for doing stuff with pine that you would have never imagined. A good place to look is the Pine Information Centre, where it has detailed instructions for using pine for gmail, advanced folder handling, and even methods for turning your incoming mail into an RSS feed(!).
By far the geekiest recent activity of mine has been using Internet Telephony services under Linux. I was nuts over skype for a while, especially given its great Linux support, but I've moved on.
VoIPBuster is a (fairly new) internet telephony service. The thing to note about it is that while it isn't quite as full featured as Skype, it offers free calls out to land-line phones in the UK, US, Canada, Germany, Australia and more.
Free, as in beer.
At the moment, land-line calls are limited to one-and-a-half minutes, but if you sign up and put on 1 euro (that's A$1.62 at the moment) worth of credit, the calls are un-timed. If nothing else, this will justify the exorbitant rates you are probably paying for broadband at home ;)
Of course, this wouldn't be any good unless it all ran under Linux. Whilst they don't provide a Linux client (but suggest one will be on the way when they get out of beta testing), you can quite happily connect an IAX-based telephony client to it, such as Kiax. The screenshot below is me giving Hiren a call in Germany for free ;)
Instructions for getting it to work on linux/mac/solaris/BSD are here. I had some trouble with the Kiax RPM packages from pbone (that'll learn me for not compiling from source); I'd highly recommend getting the binaries from the Kiax sourceforge page.