Well I have three rigs and have noticed the same thing.
Rig one is in the sig and has been running for a while, since about my join date here. I did copy the files, including distfiles, to a seperate partition, delete the old, then copy it back again. /usr/portage is on it's own partition by the way. We'll see if that defrags any and helps. reiserfs all the way around too.
Rig two is a server setup that runs folding and has /boot and / and that is all. Same thing at about 50% though. It is a 800MHz rig with 128MBs of ram.
Rig three is a Compaq Proliant 6000 with quad CPUs and 128MBs of ram set up as a server. This is a very recent install and it was slow from the get go. It hung a bit at 50% after the first sync. It to has /boot and / and that's it.
Rigs two and three runs folding and that is about it. If someone wants me too, I will post the make.conf and/or emerge info if you need it. Just let me know.
Since I am on dial-up, I have noticed that it takes longer to download all the files too. I think when I first started using Gentoo, there was about 60 or 70,000 files, there was about 128,000 last night. Seems like that may have something to do with it but I'm not etching that in stone either.
Still LOVE my Gentoo though. I do wish I had DSL though. Of course, I have been dating a lady in Mobile and may move there, they will have DSL there I'm sure. I suspect that about two weeks after I move, they will send me a email that DSL is available here.

They put A/C in our schools the year after I graduated too.

That's my luck in life. I'm one in a few thousand with my skin disorder too. If it wasn't for bad luck, I would have no luck at all. My lady is a silver lining though. She is super sweet.

I need to loose weight and she needs to gain some. She only weighs 97 lbs.

I LOVE every ounce though. I have to, there aren't many ounces there.
Later

My rig: Gigabyte GA-970A-UD3P mobo, AMD FX-8350 Eight-Core CPU, ZALMAN CNPS10X Performa CPU cooler,
G.SKILL 32GB DDR3 PC3 12800 Memory Nvidia GTX-650 video card LG W2253 Monitor
60TBs of hard drive space using LVM
Cooler Master HAF-932 Case