Tabbed, please!
I've used Visual Basic since VB 3, which only had floating windows. When I first used VB 5, which offers both floating and tabbed, I experimented with both and very quickly settled on tabbed. Now all the development tools I use except Lazarus are tabbed, and I strongly prefer tabbed: I don't need to keep clicking "View" or "Window" to find things like messages or project inspectors; and I can keep other apps un-minimised without the risk of clicking them accidentally.
I've just got a widescreen monitor (aspect ratio 16:10 instead of the old 4:3), and widescreen is superb for tabbed IDEs. Considering that one hardly ever sees 4:3 monitors in ads these days and they're getting rare in the shops, I suggest tabbed should become the default option.
Even with a 4:3 monitor I prefer tabbed IDEs. Admittedly a tabbed IDE on a 4:3 monitor restricts the width of the code editor pane, but I prefer not to create lines that won't fit A4 paper in portrait orientation anyway.