I just picked up one of these as well. I'm putting all my standard apps on it, office, youtube, dropbox, etc. The newer phones (MF9 build level) are a bear to root. However, I finally found that Odin + Chainfire autoroot did the job. My first priority was to get the sprint garbage off the phone.
My next step was to enable the the hotspot switch (please note you must have the hotspot data plan to do this).
I'm not really happy with the google now 'card' thing, and I turned off google personalization as well. They're really trying to dig into your personal details pretty deeply, and I'm terribly interested in being a profit center for them if I can help it.
I ignored removed most of the Samsung branded functions. Turned off the face recognition because it was flakey, and the same with the hand gestures. They seem gimmicky after a day or two.
I'm going to dig further in the XDA Developer threads to see what people are putting on the phone. I don't really want to put a ROM on it because some of the Samsung camera features are excellent, and I don't want to deal with messing around with the camera app apk.
Root Browser, Adblock Plus, Weather bug, Flashplayer, Quicknote, Yahoo Sportstacular, Netflix, a good E-Book reader (I like aldiko), Clockworkmod, Titanium backup and office apps were my first installations.
I need to see if there are any good overclocking kernels and apps for this phone. Juicedefender is on the list too.