This is my favourite Starbucks in the Yonge/Eglinton area. The upstairs seating area is great - it's large and has a cozy feel with the wood floor, big wood tables at the back, etc.
This is a nice contrast to all the tiny and sometimes aesthetically ugly locations in the area.
The staff are also nice, which is a bonus.
If just want somewhere to go read a book or talk to a friend it's great.
HOWEVER, if you need to go somewhere to do work that requires an internet connection, the wifi here is absolutely awful. Really really awful. Painfully slow and inconsistent awful. I have gone there about five times since moving to the area a couple weeks ago, and without exception the wifi always sucked.
I now go to Istanbul Cafe at Eglinton/Redpath if I need wifi, since their wifi has been consistently good (and I like the decor, the staff are nice, etc.).