According to the thread 3G Connectivity Issue Fix? I think I found a solution using build.prop on the CyanogenMod forum, it seems a kind of solution to the Spotty 3G part 2 issue is about to appear.
It's not clear yet if it solves completely the 3G issue or only in part or if it is just a workaround, but it seems to improve the situation. And it's better than nothing considering Google had already said « engineering improvements » had been given an end : look for post from Ry Guy (Google employee) by 4/20/10.
By the way, some of the posts head to what seems to be very serious resources about 3G and mobile networks : Vodafone 3G vs Telecom XT on GeekZone forum.