Also, do they put in a solid eight-hour day on the throne, or do they take lunch elsewhere?
The precise answer to the OP is that the Queen was crowned with the St. Edward’s Crown at her coronation in 1953 and has worn the Imperial State Crown during the latter stages of that ceremony, during the return journey back to Buckingham Palace afterwards and then each time she has opened the British Parliament (which has been roughly once every year). The only other occasion on which either of these crowns will used will be at her funeral when the Imperial State Crown will be placed on her coffin.
That has been the basic pattern in England since the seventeenth century - a coronation crown (‘St. Edward’s’) used for the crowning and a state crown used when the monarch presides over Parliament (which is now only ever at the State Opening). Earlier English monarchs had also worn their state crown on a few other occasions, usually on a handful of important religious festivals each year. But there was always the sense that it was brought out only on special occasions.
During the twentieth century it also became customary for the new monarch to be presented with the Scottish crown on their first visit to Scotland after their coronation and in 1953 much was made of this. But that crown is only presented, not actually worn. Since 1999 it has also been placed in front of her when the Queen has opened the Scottish Parliament. (There have been some suggestions that the British Parliament should follow the Scottish example and have the Queen open it only after each general election, but, so far, nothing has come of this.)
As others have pointed out, other European monarchs are no longer crowned, although some do have inauguration ceremonies. This change was part of a general trend during the nineteenth and early twentieth century. The reasons for this were usually either that they wanted a non-religious ceremony and/or wanted to stress that they were subject to a constitution/the people. Even so, some of those inauguration ceremonies - the Dutch one being the obvious example - are still rather grand occasions. Most involve a crown being displayed but not worn.
Spain is something of a special case, as the kings of Spain never did have a coronation ceremony. (Some of the earlier Iberian kingdoms did, although even then they were never as common as they were elsewhere in Europe.) They prefered to do without one on the grounds that they were kings of Spain anyway and didn’t need a ceremony to prove it.
Now that’s “musical”!! 
Could someone please explain the Benjamin Britten reference for the rest of us?
One of the better 20th Century “classical” composers, Britten wrote quite a lot of vocal music for tenor voice, which was written for and debuted by his life partner, tenor Peter Pears. “One should always sing Britten in Pears-shaped tones.” 
I presume the double-entendre in Roger Thornhill’s post becomes clear from that. An early-20th-Century euphemism for “gay” was “musical,” as when Winston Churchill, asked how a weekend with musician Ivor Novello, whose homosexuality was an open secret, had gone, responded with a twinkle in his eye, “Musical.” 
Ah, so that’s fuchsia…
Well then, on what occasions does she wear this?
the various crowns are quite heavy and some practice is necessary to get used to the weight before a State Occasion (usually the State Opening of Parliament each November). They also have to be altered for size when a new king succeeds. Most of the present Regalia dates from after the Restoration, as the Commonwealth/Protectorate had sold or melted down most of the old stuff. Many of the various jewels and crowns used in ceremonies had been actually hired for many years, not owned.
They really don’t hang out on thrones. I know, for example, that the Queen has desks she works at (equipped with hooks for her handbags - no, not joking), when she’s not dashing madly about trying to get to all her state occasions. Her schedule is actually packed; furthermore, she herself is quite committed to reviewing matters of state and discussing them with the Prime Minister, and her long service makes her probably the single most experienced government official in the realm. And from what I’ve heard, Charles wants to take his government duties even more literally than she.
When she goes to the roller derby.
Probably the oldest current part of the regalia is the Anointing Spoon, which was one of the very few items spared in the Protectorate, and probably dates to the twelfth century.
I didn’t know this about “musical”, Poly.
When I heard the “see under Pears” joke for the first time, a discussion ensued about whether it shouldn’t be the other way round. Or, the other side up, or whatever.
I see the King or Queen also gets a ring. There aren’t eight more are there?
So, is the crown used on Ontario highway signs a representation of a specific real crown?
It’s a heraldic depiction of the Crown of St. Edward.
For a good picture of the real thing, go to Squink’s link, and click on the icon at the bottom of the page that says “Click to view other Crown Jewels”