Brian Harring (ferringb) has some really slick patches posted on his blog for some serious speedups in Portage.
The first uses confcache to cache those pesky (and redundant) tests during ./configure. Nothing quite like watching the test fly by at warp speed… ;)
The second implements background fetching of source tarballs during an emerge. Need I say more?
The instructions for using both patches are included with his posts, and I’m using both now with great success. Rock on ferringb!