Baya87

If people can get by with a single speed bike, a 7 speed (Fuji 13-34T 7-speed ) should be fine for pretty much everything else, no?

If I am not a racer, but I commute to work everyday with my hybrid and am interested in occasional longer distances (50 miles/day), will I be ok with my 7 speed (just bought it)?

What are the benefits between single speed vs. a few gears vs. lots of gears. Are lots of gear overkill or would they be useful to a semi-casual rider like me?

LesterOfPuppets

Depends on how fast you want to go and the topography of your neighborhood. For a 13 in the back, I'd want at least a 48 up front if I was riding flats all the time. My commute is flat, so a single speed is fine. However, if I wanna go downtown, which is separated from my neighborhood by a deep creek valley, I gotta have gears. I'm too old to go without.

SS is pretty low maintenance compared to multi gear. Lots of gears are generally overkill unless you go up very steep hills or carry heavy loads. I tried 8-speed on my MTB for a bit, but had to go back to 24-sp to get up this one 30 degree hill on a local trail.

DannoXYZ 

Depends upon your terrain and fitness. Single-speed is fine if you live in a flat town. However, it's still not as optimal as a geared bike because you still need to accelerate from a standstill and need to account for top-speeds.

Don't know what kind of shape you're in, but 50-miles/day isn't exactly easy, nor is it tough. If you want to cruise along at 10-15mph, you can have a single-gear for that speed. However, as you go faster and faster, the range of optimum RPMs at any given speed gets very narrow because you have to balance your cardiovascular system with your muscles and get just the perfect balance. This typically requires hitting a sweet-spot of 85-95rpms. A wide-ratio 7-speed will most likely have only one gear that falls into this spot at your cruising speed.

Sure, you can get a single-speed with just that exact gear. But the accelerations from a stop will hurt your muscles more than necessary and will result in for muscle-fatigue and soreness for that same distance at a slower average-speed.

Personally I like as close-ratio gearing as possible to optimize cruising speed. I would like to have a 12-24t straight-block with a 34/50t crankset. That way, I can have the best chances of finding the perfect, most efficient gear at any given speed.

Sci-Fi

13-34T 7-speed is good enough for most conditions and people. I would guess the chainring/chainwheel on your Fuji is around 44t. An 11-34 7-speed cassette/freewheel will give you wider range and more top end. "More gears" depends on what you want/need the bike to do...like a lot of hill climbing or for steeper hills, more intermediate steps in gearing to find that 'right gear', or to go fast on the flats. There's no right answer that fits everybody or any riding condition. It's a compromise. A few will buy/tailor their cassette (and front chainrings) that best fits their needs. Even with just 7-speeds, there will be gears that you rarely use. As far as single speeds, there are some that ride anywhere/everywhere and others that feel short distances or flat roads are best for that configuration...most will opt for more gears, whether it's a dérailleur system or IGH.

Your bike should handle a 50 mile ride just fine, but I would suggest working up to that mileage. Might find you need a different saddle or adjustments for better comfort and/or more efficient pedaling position. Plus your bike is new and some cable stretching will occur that 'may' require a followup adjustment from your LBS.