If you OG was over 1.035 you probably didnt pitch enough yeast. You should always be using a starter with liquid yeast. The starter will get the yeast activated (ready to consume wort and thus decreasing lag time) and will increase the total cell count (and therefore decrease lag time.) This is true for all the liquid yeast strains, and you should always do a starter, even if you are pitching multiple vials/smack packs.
If your gravity was higher than 1.050 you probably only pitched about half of the yeast you needed, and that's if the vial was fresh. If it's older than 3 months from manufacture it's probably half dead. There's about 100 billion cells in a vial at manufacture date, but that cell count decreased by about 20% per month. It'll almost never reach 0%, there will always be some yeast in there to culture up, but as far as pitching directly into a batch of wort, there's not really enough yeast in one vial for anything but Mild, lite Cream Ale, or something small like that. There are yeast pitching rate calculators out there like Mrmalty.com, and some others, but use that as a starting point for how much yeast you will need to get your batch going healthy. You should have some lag time (time from when you pitch yeast until you see activity) because this is where a lot of flavors are given off by the yeast that are a part of good beer, but your lag should be in the 6-12 hour range, not 48 hours.
If you are going away, I would definitely pitch another vial if you havent seen activity yet. You will most likely see some activity soon from what you have, but the yeast will be stressed out, and probably wont ferment your batch to expected terminal gravity.
