If you are used to using RAR on your desktop computer, you have to get it on your PDA too. Nothing special about the usage, all the basic functions are available. I also like the file explorer of WinRAR, which is not, like the WinZip one, limited to the compressed files themselves, but can serve as your standard file explorer (with the advantage of browsing through RAR files as well). The only downpoint is that it is not possible to sort the files by their extension before selecting them.
And the best thing: if you don't have the Resco File Explorer (which manages ZIP files): PocketRAR can also be associated with ZIP files, just like it's bigger brother on Win32.
But all in all, a great freeware which is definitely a must-have, even though the speed when working with compressed files is not really convenient.