Advanced Techniques
there is a trick to get by glass and some other obstacles by shooting a portal next to it, then shooting one on top of the first. the second one then moves on the other side of the glass letting you get past it. here's a screen. i've seen this give some mappers some trouble.
[img]https://webspace.utexas.edu/mfh236/www/shmitzchamber_01_beta_0_1_20001.jpg[/img]
I'm not sure that trick will work when the SDK updates, because the compiler will be smarter about what does and doesn't count as a distinct portal-able area. But, you might still be able to make a map with it in mind.
(I just totally fixed that, by the way ;P)
actually i remember something like this back before anybody was making custom maps. i never understood how it had worked until now, but i think it will indeed work even with the official sdk (and the working non-portable textures).