Terminal Windows: xterm windows might look like they are not redrawing correctly, but they are in fact. It is up to the program running inside it to detect window size changes and redraw the screen as necessary. One way to deal with this is to run screen inside the xterm, as it will handle resizing and redrawing correctly.
Size Hints: The PResizeInc and PMaxSize hints are honored. PMinSize is not, as it might have problems fitting all the windows in when tiling them.
Resizing Windows: For windows that do not cope well with being resized, you can disable automatic resizing on a particular desktop, making the windows in the right track be stacked on top of eachother instead. This can also be used for windows that resize slowly, like Netscape, to speed things up considerably.
Multi-Head Displays: It does work well with multi-head displays. One of my development systems is a dual-head Sun Ultra2 running Solaris 8, so this functionality has been tested quite alot. It currently behaves in a predictable manner when you switch focus between screens, move between desktops etc.
GTK Applications: Some GTK apps do not set WM_TRANSIENT_FOR correctly on their dialog boxes, and they also sometimes have a different class string on those subwindows, making things confused. The best way to deal with those kinds of problems is to specify both the class and instance of the top level windows you do want tiled.
Standards Compliance: At this time there is no GNOME/KDE/Motif/whatever compatibility, although it is possible that will change some time in the future. For now, it follows ICCCM as much as it can while still providing all the automatic functionality that it does.