If the mashup embed works, it will show up below ( it shows up fine in Windows Live Writer Beta 2).
Well. I tried. Although the embed is in an IFrame ( i.e, no javascript), it does not show up in WordPress. Which is nonetheless disappointing, and one of the disadvantages of having this kind of setup.
In any case, Popfly works great. I created a photostack that grabbed random Blaugh comics in a couple of minutes. Worked great. So simple to use.
Back to creating mashups. More soon.
Random Musings 
Did you get a specific error? Can you send me the link to the page which has the embedded iframe so that I can see what’s going wrong?
Thanks,
Sriram Krishnan
Popfly team