I'm personally not entirely overwhelmingly in hate with the way blood works right now. My dwarves inside the fort clean the place up rather nicely before too long. I have a couple dwarves who I don't bother giving any tasks except clean and they keep the place pretty sparkly. It also helps that I've smoothed every exposed surface, which encourages them to keep things clean. Gunk outside eventually gets washed away by rain. I haven't embarked in no-rain areas, so I expect that could get really annoying and it would probably be a good idea if blood and gunk would decay after a while in those cases.
But there are two things that really, really need to be fixed:
1) Blood in water never goes away. Getting anything in water is only a guarantee that it will multiply indefinitely. If you embark on a frozen location, snow/ice counts as water. Anywhere you have snow/ice is going to be permanently and forever coated in a thick sludge of anything you've ever killed. That's just wrong.
2) Pets can never get blood or other contaminants washed off. I've been using the "dipping pool" method where I have a short trough between my meeting hall & food storage area and the rest of my fort. Every dwarf has to go through it to get food or booze. My dwarves are all shiny clean. They track the crap out of the pool, but like I said, my dwarves generally keep it pretty clean because it's built very near the meeting area. However I've examined pets on one side, covered in 11 pages of gunk. They step into the pool and I pause. While they are in the pool they only have "Water covering" over all their body parts. When they step out of the pool they are coated in water plus a coating of every single contaminant that is currently sludging around in the pool. Even if you can somehow clean your washing station of every contaminant currently floating around in it and replacing it with clean water, as soon as a pet steps in, it's full of crap again, ruining all your hard work.