One of the first questions people typically have is "Am I expected to tip the magician?" The answer depends entirely upon the setting.
Of course, in a theatrical setting, where the magician is performing on stage, tipping is uncalled for and would be entirely out of place. You've either purchased a ticket for the show, or your host has paid an all inclusive fee to have a performer at your event.
If it's at a private function, but more of a walk-around, casual setting (ie., the magician is hopping from table to table, or is mingling with guests at a cocktail party), we begin to enter into the area where people don't know what to expect. Generally speaking, it's safe to assume that at any private function, the magician has been well-paid for his appearance and tipping is unnecessary. If you feel you've received exceptional treatment and want to show your thanks, a tip may be accepted, but you should feel under no obligation. The magician is not expecting a tip at this type of event, and receiving one is the exception rather than the rule.
If you feel you want to offer a tip but are still unsure, I would advise you to consider the type of event you're at. If you're at a wedding, or other type of "special" event, I would consider tipping out of the question. Were I offered a tip at such a setting, I would likely turn it down, not to be rude to the audience member, but to be polite to the bride and groom. At a casual cocktail party, I would certainly never expect a tip (if I'm performing in such a situation, it is literally the farthest thing from my mind), but would be far less likely to refuse it if offered.
Again, feel under no obligation, but if you have a strong desire, just use common sense.
If the magician is performing at a restaurant, hopping from table to table, we find ourselves in the situation where people become really uncertain about the proper etiquette. A magician working in such a situation should be financially taken care of by the management of the restaurant and thus should not be soliciting tips. In fact, I consider those performers who actively solicit tips (such as by wearing "I work for tips" buttons on their lapel) unprofessional and rude (and therefore, perhaps somewhat paradoxically, much less likely to receive a substantial tip from me). But if the magician is not rudely soliciting tips, you might wonder if it's customary to offer one.
The answer is that tips are welcome but not necessary. Though these performers are well paid by the management, they're not receiving the same level of pay they would from private functions (most restaurant performers work only a few nights a week and are available for private functions on other days), and tips are a nice bonus.
You should feel under no obligation to open your pocketbook if a magician happens across your table. In fact, if tipping the magician is going to cause you to lessen your tip for the wait staff, I would advise against it most strongly. Though the magician may be grateful for a little extra money, the wait staff actually work for tips. The magician's hourly wage is substantially larger than the waiter's. But once the wait staff are covered, if you still have a little money for the magician, it's certainly appreciated (but again, not necessary).
I would say, in a restaurant, if you enjoyed the show and the magician was not rude, it would be appropriate to offer a few dollars. If you really can't afford it, though, just enjoy the show and don't worry about it. The magician is probably counting on receiving some tips, but is certainly not expecting them from all (or even a majority) of the tables.
Another way to show your thanks is to make sure and pick up the magician's business card and keep him in mind for your next private function (or tell a friend who may be seeking entertainment). Even more than tips, magicians count on these private bookings (many of which may come from having performed for someone at a restaurant) for their livelihood.
The only situation in which I would consider tipping to be strongly encouraged, is if the magician is busking, or performing on the street. In this situation, he has received no hourly wage or up-front compensation for his time and labor, and is relying entirely upon the generosity of his audience. So if you watch a busker's show, and have a little cash in your pocket, by all means drop it in his hat.
Would I consider tipping mandatory, even for a busker? No. By contrast, I would consider it mandatory for a waiter or valet (by which I mean to say, I consider it extremely rude not to tip these people, unless they've provided truly horrible service). However, the busker needs to feed his family, and the only money he's getting comes in the form of tips.