Just checking now it does look like the yahoo login page is encrypted, but whatever you do after you log in is not. So they can't get your password, but they can see everything you do after that.
Yes they can get your password if they want, like was mentioned in another answer most likely they will not, however they will in today's day and age keep a record of every site you visit.
Like was also mentioned your biggest threat of password theft is from a hotel, Starbucks, etc. Google 'Monkey in the Middle attack' and you will see this easily defeats SSL and HTTPS.
Well now-a-days, when even top secret websites of governments and defence are getting hacked, we can not be sure of anything. It can depend on the organization policy, as some care if people are using office for personal uses, while others are lenient. Moreover, some networks like to spy on others working while others do it only to restrain harmful/illegal surfing.
But the best way is a) to have a strong password or b) password protect your PC from illegal access. Please see following links:
