Why is there a watery run-off after cooking my bolognese?
A few things that can help, if it's not an issue with fat like @Aaronut suggested:


Tomato paste.  Yes, I know it's a sacrelige, but it'll act as a thickener.
Take the pasta out before it's gotten to al dente, and finish cooking it in the sauce; the pasta will absorb any extra liquid, and help to thicken the sauce.
Do not rinse off the pasta after you drain it.  Way too many people do, and it washes off the starch that you want for the sauce to bind to the pasta properly, and may introduce extra water.