I recently purchased a combo drive from Mac-ResQ, installed it myself on my 667 MHz TiBook (Gigabit) and it works splendidly.
BUT...
not only does the bottom case not fit correctly around the optical drive area (I understand getting the bottom case to sit right again is a common problem), there is also a slight BULGE around the drive area as I run my hand over the bottom of my 'Book.
Anyone experienced anything like this? I did notice that there is a thin strip of foam-type material adhered to the bottom of the new drive (nothing was on the stock drive)...but it seems like the ResQ drive itself may be too big for it's little home there.