I have a T1i with no lens and was looking at 50/1.8 or 1.4....I've heard that the 1.4 has AF issues...Is there much of an appreciable difference that an average casual person would notice or need in the 1.4?
I haven't had any problems with either the 50mm f/1.8 Mark I, II or the 50mm f/1.4. Then again, I have never owned a Canon Rebel before.
The primary reason (other than the fact that it is a prime) for pairing it up with a walk around lens is for the faster aperture. Typically for zooms, you either have a short fast zoom like the Canon 24-70 f/2.8L or a slower zoom with longer range like the 18-200, 28-135IS, and 24-105L. A lot of people have complained that the short zoom is too short and too heavy. Yes they are the bread and butter of let say a wedding photographer but for the typical traveler many found them too limiting. This is the type of person who is lugging around a lot of other stuff (especially with children) who won't necessarily get family to pose for them at a whim or make the entire family wait while they climb that wall to get in closer for a better shot. They have a lot of other intentions rather than traveling just for photography. On the other hand, these zooms may be a pain in the rear end once the sun sets or indoors. That's when you pull out the 50mm prime....
When I travelled with family, I carried two bags both packed into a Pelican. One had 24-105L + 50mm in a small shoulder. The other a slightly bigger bag with 24, 50, 85, 135, sometimes 300L. If I'm out with the family, I carry the walk around zoom + 50mm and often take note of locations of interest. At times, I'll head out on my own (wife permitting.. hahaha) to really focus on pictures. That's when the bigger bag comes out and the tripod comes along. This is what I found to fit me...
When my son was born, I swear for the first year I rarely used anything else but a 50mm. Its all I could handle with the stroller and diaper bag. Small, compact, wide range in apertures, and its not like the baby is going suddenly jump up and run off to the playground.