The main advantage of portable applications is that it lets you runs application without having to install them to the PC. By just copying them into the thumbdrive, you have carry the usb drive and run it on any computer.
This makes trying out new applications very easy and simple without leaving trails of registry rubbish and leftover files and folders.
I had been using PortableApps for a few years now. Although the quality is high and regularly updated, the collection of applications available is sufficient but not wide.
Recently I started to try out CodySafe which hasa collection of administrator tools that I find pretty useful. Look under Download, Portable Suites, Admin Pack.
This actually got me interested in also testing out other collections to see if there is anything interesting, especially for use in a small business setting.
Will be updating anything interesting here… stay tuned.