After playing with RELENG_6 for a while, i can now safely says that the new upcoming FreeBSD release will be a very good release(TM)! Altogether, the operating system is very stable and have a good responsiveness.
But... my main problem encountered with my laptop still remain: a long standing problem with the GigE Ethernet driver re(4). See Problem Report kern/80005 for more information on that subject. Just note that the problem was not solved (nor changed) trying the new polling(4) operational mode, nor trying the development branch of FreeBSD: 7-CURRENT, as somebody had advised it to me in the past... Too bad.