Seeing the difference now isn't the reason to save photos as PNG. PNG uses lossless compression, while JPEG is 'lossy'. What this means is that for each year the JPEG photographs sit on your hard drive, they will lose, on average, roughly 200 bits, assuming you have SATA - it's about 120 bits on IDE, but only 5...10 bits on SCSI, due to rotational velocidensity. You don't want to know how much worse it is on CD-ROM or other optical media.
I started collecting JPEG pictures in about 2001, and if I try to view any of the photos I downloaded back then, even the stuff which was saved at 100% quality and 4:4:4 chroma subsampling, they just look like crap. The shadow detail is terrible, the highlights...well don't get me started. Some of those photos have degraded at a rate of 100 or even 150 bits/year. PNG pictures from the same period still look great, even if they weren't stored correctly, in a cool, dry place. Seriously, stick to PNG, you may not be able to see the difference now, but in a year or two, you'll be glad you did.