Just replaced the HDD and the cd/dvd.
Got the Hitachi 100GB 7200rpm HDD and a Panasonic DualLayer DVD-burner.
Replacing them took about 3 hours,taking my time and having a cup of coffee.Just get the guides from iFixit or tuaw.com and print them.
And use two sided tape for the srews on the layout that you draw when you take your computer apart so you dont loose them...
If you are tecnically inclined at all,it is a no-brainer to do it.
The performance is up and the book is a blast to use now.I noticed a tad higher temperatures but nothing concerning.Battery life doesnt seem to be affected at all,as it shouldnt.Apparently the Hitachi boys have done a good job ,as few other posts have noticed.
The only gripes that i the HDD apparently is left spinning (idle?) when put to sleep.It emptied a 50% full battery when on sleep during the night (shell open position).But, when in shell closed position and in sleep mode the battery apparently lasts longer...
But all this is isnt verified at all, i have to run some tests here.It is just a hunch.
In short : If you need to keep the computer for whatever reason,like I did, then it is ok to change the guts.
Otherwise sell it and get a MB or MBP, since the HDDs,drives and memory aint free.
Or unless you are a bored mofo like me who likes to poke and tinker with things.