For the blonde, pale malt is a little sweeter and will give a little more color to the beer. Pilsner is a little crisper and, like Beerriffic said, you have to watch out for DMS. I have made some nice beers combining the two, usually along the lines of combining two parts U.S. pale malt with one part Pilsner malt. You still get a little crispness from the Pilsner, and you do not have to worry so much about DMS. A 70 boil is plenty, and the extra 10 minutes might not even be necessary (but that's what I've always done, at least).
For the porter, I doubt anyone could tell much of a difference between pale malt and Pilsner, depending on the rest of your recipe. If you go 100% Pilsner for the base malt, you will lack a bit of malt character, but the biggest difference will be with DMS. You definitely have to watch out for it, there. Plan on a good 90 minute boil.
TL