Hi guys - it's been a while...
I've been playing about with Inkscape
a little recently (though without my Wacom ArtPad - the power brick has gone AWOL), and came up with a quick trick for quickly creating speech-bubbles:
1. Open the Layers window (Layer -> Layers... or Ctrl-Shift-L) and add a new layer. Call it "Speech Bubbles" and set Position to "Above Current". Create another layer called "Speech Bubble Text" and set its position to "Above Current" too. Select the Text layer and add your text, then switch back to the Bubbles layer.
2. Draw two or more bubbles around your text using the standard tools -- ellipse, rectangle, etc. -- don't worry about the colour for now. Overlap them where you want the bubbles to combine. Add small arrows from the bubble to the relevant character by adding a triangle using the Bezier Curves And Straight Lines tool (Shift F6). Make sure you click the first point at the end to close the path.
3. Select all the bubbles in a particular group (i.e. what one character is saying in one particular panel) and select Path -> Union (keyboard shortcut is Ctrl-Shift-= -- i.e. Ctrl-+). Do this for all the bubbles. Alternatively you can apply Path->Union to all your speech bubbles, but then you won't be able to change them individually later. To maintain more control, duplicate the layer (Ctrl-C, New Layer, select the layer, Ctrl-V, hide the original layer -- unless there's a quicker way) so you have a copy of the file with the original, editable bubbles.
4. Select all the bubbles, then set the Fill Colour to white, and Stroke Colour to black. Play with the Alpha (A) slider on the fill colour to adjust the opacity of the bubbles if you like, but in my opinion the good ol' white solid background and black solid line works best.
For transparent / shaded bubbles - duplicate the layer, and when you apply a fill colour (step 4), make the bubbles transparent. Switch to the layer copy (which should be below the layer with the transparent bubbles) and make all the bubbles white with Line Style set to "None" (this is in Object -> Fill and Stroke -- Ctrl-Shift-F). Play with gradients and transparency as required
And last but not least, if you're using a Wacom or similar tablet with pressure sensitivity, you'll probably want to make Inkscape use it. To enable it, select File -> Inkscape Preferences (Ctrl-Shift-P), select Misc from the list on the left, and make sure "Use a pressure sensitive tablet or other device" is checked. If it isn't, check the box and restart Inkscape.
Bonus question - is anyone else using Inkscape, or just me?