I used to start games at level 3 and then make them earn all the XP to advance to level 4. I did this because I felt that level 1 and 2 characters were simply too weak, and between their overall lack of resources to spend on healing potions, and the frequent breaks they would have to take to heal up before adventuring on, the first couple levels were too much of a drag to bother with.
I've been using the Max HD + Con stat for starting hit points, and then started the PCs at the beginning of Rise of the Runelords, and worked out fairly well. What I found was that with increased HP, they were more likely to survive, which is good, but they were actually having a little too easy of a time with the adventure, so to counter this, I upped the difficulty of the encounters a bit to compensate.
At second level, the increased hit points were somewhat less noticeable, so I didn't compensate as much. By third level, it was hardly noticeable at all, so I ran things straight out of the book.