The 8-bit color limitation issue is well-known and has been for a long time. The solution is GEGL (
http://en.wikipedia.org/wiki/GEGL), which has been under development for a (very) long time now and is partially implemented in GIMP 2.6, the latest stable version. It
is a problem, but it's important to put it into perspective: almost all monitors display 32-bit color (EDIT: or less) anyway, so if you're doing work targeted at a computer screen, it probably doesn't matter anyway. If you need to do work at color depths higher than 8 bits per pixel (that is, if you're doing serious print work) then yes, you need to be aware of these limitations. If you're almost everyone else it's probably not an issue. (I don't mean to imply that it's not a problem at all, but I think it's important to keep it in perspective.)
For the people here asking whether GIMP is good enough for what you're doing: Ars Technica did an excellent review of GIMP 2.6 about a year ago (EDIT: 2 years, but it's still the same major version). It's long, but well-worth reading and will answer your questions. It's written from the perspective of a professional who uses Photoshop, but does an excellent job of remaining balanced. This quote summarizes the review (and also my opinion) pretty nicely, I think:
I may seem to skew negative since I talk so much about what's missing, but
it's hard to dwell on what a program does well and not sound like a fawning
idiot. Most people who sit down to get image editing work done with GIMP
will not be disappointed. There is a ton of room for advanced work here.
It can be found here:
http://arstechnica.com/open-source/reviews/2009/01/gimp-2-6-...While I don't follow it closely enough to really discuss GIMP's current development status, development does seem to have slowed significantly (purely from a user's perspective) in recent years. This is a real shame, since I think that for the most part it's an excellent program and in general I much prefer to work in GIMP over Photoshop. For all of its many flaws, I think it's a fantastic piece of software.