I have 9,942 photos totaling 104GB in approximately 40 folders on my laptop's hard drive. I routinely keep the last 3 years on my HD and keep all of my photos on an external drive. The Hard Drive is just a storage unit, just like a CD or DVD, only it's magnetic. It will run fine at capacity. Maybe it's slowing down my system a little, but I have no real problems with speed. My 500 GB HD is about halfway full.
MBP, i5, 2.53 Ghz, 4 GB ram, 500 GB HD.

So I guess my answer to your question is no, I wouldn't worry about it. Unless your HD is nearly full and there is no room left to swap files, it shouldn't have any problems storing the amount of data it was designed to store.