Linux

In some networks, computers have to be registered to get connected. Upon registration, the computer will receive a name and an IP address. Every time it connects to the network, the DHCP server assigns it the same name and IP address. The DHCP server identifies computers based on the MAC address, which is unique to every NIC. However, if you know the MAC address of a registered computer, you can use it to connect to the network, faking the MAC address:

I am using Textco's Gene Construction Kit (version 2.5) do draw my DNA vector maps. Unfortunately this company doesn't care about Linux users. Therefore I have to use WINE to run the Windows version of the program. Admittedly, I could run VMware, VirtualBox or Parallels, but all that just to run a small program? Unfortunately either the Gene Construction Kit (GCK) is not coded according to standards or WINE is still not able to deliver full compatibility but now and then a WINE upgrade renders the program unable to run.

If I install a new computer for myself (or if I do a fresh reinstall on an old machine), I want the computer have the software I am used to. To automatize this process, there a different approaches. If you use Ubuntu, you can use Ubuntu One to syncronize your software selection across many different machines (starting from Ubuntu 11.10 Oneiric Ocelot). If you use something else, it is getting tricky. You can use the following commands to generate a list of installed packages and load the list later for installation:
dpkg --get-selections > installed-packages.lst