I had a very pleasant experience donating a few suitcases full of clothes. I called in advance to see if they took sheets and duvets (which they do) and the phone was answered very promptly.
When I arrived they had automated doors which made it easier for me to pull my stuff in. I spoke to at least four employees while there and each one was polite, friendly and helpful. They gave me garbage bags, offered to help me put my stuff in bags and sincerely thanked me for my donation. It definitely made me feel appreciated.
The store itself is very clean, spacious and well maintained. I've been in plenty of thrift stores before and some can feel crammed and musty, not this one. It would be a pleasant shopping experience for those who frequent this store.
Also of note: they have a parking lot, they steam and clean the clothes before they go out for sale and they will collect furniture or large donations from your home. The proceeds via the Yonge St Mission go to a bunch of community services. Also, the store itself provides jobs and training for disadvantaged, low income Toronto residents.