If I were to use LaTeX to make a poster (if Illustrator would somehow suddenly vanish) I would probably use TikZ in overlay mode to have have great control of positioning and interplay of graphics and text. I might use something as low-level as \hbox to \somewidth{\spaceskip 10pt plus 100pt\relax T I T L E}
for text that shall spread to same boundaries, so that it is perceived as a block. There would also be a lot of fiddling with \parskip
and \lineskip
(to bring back order in a space filled with many font sizes) and going from editor to the pdf viewer and back, until I would be satisfied with the graphical output. Basically A LOT of tweeking - but that happens to me even when creating a normal A4 layout.
Good fonts are of the utmost importance (may I never again see a poster in Comic Sans that presents any serious matter - or any other matter, for that matter). Usually sans serif fonts are best due to their readability. I have learned that I just can't get away with only typical regular and bold weights, because regular is too heavy for many poster applications. A light version of the font comes to the rescue. Light+Bold and sometimes Regular+Black work well together because of contrast, and contrast is very important. A poster should read in half a second and allow the viewer to become a reader and discover the secondary layer of information (like organizer, subject and registration address) and then tertiary layer (main programme) and then there are some descriptions and less important info.
This all can be done well in LaTeX without doubt, but requires lots of visual checks during the process. Nothing in the layout should be left to pure chance or even some package defaults. Typesetting a design in a program without instantaneous visual feedback isn't the easiest task.