are leather jackets warm enough for winter?

and what should i be looking for when buying a leather jacket....

probably not in toronto. i find them most useful during fall and winter. summer they are too hot and make you all sweaty, and in the winter they don't block out the cold winds.

look for soft supple leather, not one of those like faux leather, or sketchy kind of cardboard like leather.

It depends.
If you are doing a lot of walking or public transit which includes waiting for buses for half an hour,
then a leather jacket will not do the job at all. You'll freeze.
I have a leather coat with hood, which has a thick removable lining, and on days where the temperature dips below -30C (don't forget windchill) my leather coat barely does the job.
Even with the hood I still need a hat & scarf.
If you are driving a car, then still, I would not recommend a leather jacket. Leather feels like the ice itself, and, in my opinion, is more suited for spring/fall wear. What if your car dies on a bitter cold day or night? A leather jacket will not protect you enough from the elements.

I don't know what your budget is, or if you need a winter coat to accomodate a suit underneath,
or are you wearing streetwear underneath?
if you insist on leather, I recommend you get a proper leather coat that well-covers your butt.
Make sure the coat has a thick removeable lining and a removable hood.
When you try them on, think also about how the pockets are arranged. What I mean by this is,
that the coat also have high pockets in case you lost your gloves, you can tuck hands in the upper pockets.
Also make sure the coat has strings to tighten the hood, mid section and bottom of the coat.
These features help to make it wind-proof.

Danier makes decent coats. Or, if you want to go for a nice drive to Acton Ontario, check out the Olde Hide House. It is famous for their leather coats.
There are also stores/outlets on Orfus Road (near Yorkdale Shopping Centre) that carry leather coats.
If you are on a tight budget, you may also try the thrift stores. They seem to have a lot of leather coats & jackets at any given time.

What I really recommend you buy for winter is a down-filled parka with hood that wraps around your face..
Marks Work Warehouse used to carry those giant parkas with hoods.
They were down-filled and keep you warm and snug even in the most bitter cold weather.

^ Some good advice in the post above.

I would say no, leather jackets are not really warm enough for winter on their own. I guess it gets a lot colder in Toronto than it does in London. If you like the look of a leather jacket then layering is the way to go; perhaps wear it over a well fitted cashmere sweater. Of course you could get a lined jacket, but then that would restrict you to wearing it only when it's suitably chilly.

Personally I like the softer Nappa leather; it feels less restrictive and doesn't weigh a ton. I have the "George" jacket in Nappa Digos by the British firm Lot 78. Serves me well in the winter over a sweater or cardigan; cool enough wth just a shirt or t-shirt in the spring.