Miter joints, like butt joints, need to be reinforced to be useful. If you can think of a way to beef up a miter it's probably already been done.
Very seldom will you find a joint that hasn't been beefed up somehow. Besides just glue I've seen miters that have been half-lapped, biscuited, had butterfly inserts, splined, doweled and the list goes on.
Woodworkers go to the effort of using beefed up miters because these joints look best in certain applications.
Decorative picture frames would be very hard to make using any other joint. Cabinets use doors with mitered frames for looks and production efficiency. Decorative trim in houses are installed with miters strictly for looks. The same goes for furniture.
Nails, Screws or Dowels - Driving some type of mechanical fastener through the outer edges is ok to do if you can cover it up with filler and finish.
Dowels - Spanning the joint thru the middle is quite common if you can drill the dowel holes accurately. Using a positioning jig to drill the holes is a must for a straight joint.
Loose Splines - These are more forgiving than dowels but you still have to have a good way to cut the grooves for the spline accurately. Although you can use a table saw I prefer to use a router and table for more accurate grooves.
Pocket Hole Screws - The great thing about pocket hole joints is the fact that you can keep working without having to stop and let glue dry. It's also a very tight and strong joint.
Biscuits - Biscuits are a good solution for alignment and strength. The down side would be the time it takes for glue to dry.
Corrugated Fasteners - Are used to hold joints together while the glue dries and is also used to repair broken joints. These fasteners are seldom used anymore as there are several ways to beef up a joint that's definitely a better choice.
Half Lap - A variation of the standard miter joint. The miter is only cut half way through each piece and the other half of the thickness becomes the glued up area that holds the joint together.
Butterfly Inserts - A key or insert that looks like the wings of a butterfly. This insert is embedded across the joint to strengthen and hold it in position.
Plated Miter - One or more plates screwed to the back side of the miter is another option to beef up the joint.