However, the advantages of using a Japan Rail Pass depend a lot on your trip's plan, so here are some calculations to help you decide for yourself:
Currently, the prices for a simple (non-first class) JR Pass are:
for 7 days: 28,300 Yen ~ 300 US Dollar ~ 234 Euro
for 14 days: 45,100 YEN ~479 US Dollar ~373 Euro
for 21 days: 57,700 Yen, ~612 US Dollar, ~477 Euro
And here are some prices for the most commonly used Shinkansen lines:
Tokyo - Osaka, Distance: 556.4 km
Total: 14,250 Yen (Fare: 8,510 Seat Fee: 5,740), ~151 US Dollar, ~118 Euro
Tokyo - Hiroshima, Distance: 894.2 km
Total: 18,750 Yen (Fare: 11,340 Seat Fee: 7,410), 199 US Dollar, ~155 Euro
Tokyo - Kyoto, Distance: 513.6 km
Total: 13,720 Yen (Fare: 7,980 Seat Fee: 5,740), ~146 US Dollar, ~114 Euro
What better image to illustrate these calculations that this pair of Shinkansen trains...
EXIF info:
Nikon D90
Lens: VR 18-55mm F/3.5-5.6G
Focal Length: 18mm
Aperture: F/7.1
Shutter Speed: 1/1000s
ISO Sensitivity: ISO 500