No matter what distro I'm using, it's common for me to use applications that are not native to that distro's desktop environment.
Right now, I'm logged into Mepis 11. The default environment is KDE, but I'm logged into a Fluxbox session. Here, I prefer to use xfce4-terminal instead of Konsole because Fluxbox's transparency works with xfce4-terminal, but not with Konsole.
Mepis 11 comes with Firefox. I prefer to use Chromium, but the version from the repos is still at 13.0.782.220, so I installed google-chrome-stable (now at version 21.0.1180.75) from outside of the repos, and I use that instead.
KWrite is the default text editor, but I prefer to use Geany.
For file management, KDE has Dolphin, which I use most of the time, and Konqueror. But I also have Thunar (from Xfce) and PCManFM (from LXDE) installed.
I don't use either of those very much, though.
Gwenview is the native image viewer, but I also like Geeqie and Mirage.
The idea is to use what you feel is the best available tool for the job. Linux gives you tons of choices; you don't have to only use applications that come with your distro's default desktop environment.
Unless you really want to.