Sawzall, both my brothers have worked as mechanics, have owned Snap-on, Matco, and MAC tools, as well as some of the cheaper tools. One brother was a Matco distributor for about 5 years, and I repaired/rebuilt mechanics' air tools for 3 years, so I've had a little experience in this area. I think most non-professional mechanics would be amazed if they knew how much money good mechanics have invested in the tools of their trade. I'm just guessing, but imagine it's $15,000 to $30,000 for most professional mechanics (a good toolbox alone will cost about $4,000 and up. I know mechanics who have toolboxes that cost $16,000 - not including the contents). For the typical homeowner or do-it-yourselfer, I personally think it would be foolish to buy Snap-on, Matco, or MAC tools unless it's a specific tool you can't find elsewhere or you find a good deal on a used one. Snap-on was probably the first to have the "rolling showroom" trucks calling on the garages, then MAC and Matco (which at one time was all one company before they split), and you'll probably find those three just about everywhere, but now you also have Cornwell, Craftsman, and a number of independent operators in the field.
The discount tools you find in the box stores may or may not be good enough for you; depends partially on whether you're talking about hand tools ("hard iron" in the trade) or power tools, who made them, how you use them, whether you can get parts if they need repairing, etc. You'll have to decide for yourself.
Now I don't know enough about all the brands, but I can tell you that as far as Snap-on, MAC, and Matco are concerned, one is no better than the other. They all three sell good tools, and they all three occasionally come up with a "lemon". So, like buying a tractor, the dealer may be more important than the brand.
There are several reasons that mechanics buy their tools from the trucks that call on the garages (in spite of the fact that their prices are very high):
1) as has already been mentioned, they will have some specialized tools that you won't find in the stores,
2) that truck shows up once a week every week - usually at the same time and day each week, so if you have a tool break, you don't have to take it somewhere to get it fixed or replaced, just give it to your dealer (or distributor as most are officially called),
3) perhaps the biggest reason is that the mechanics usually do not pay outright for their tools. The trucks all run truck accounts (revolving charge accounts) and the mechanics pay X number of dollars a week - another reason you know that truck's going to be there. Whether anyone buys anything today or not, the distributor is going to be there to collect his weekly payments,
4) "braggin' rights". Let's face it, humans do that. /forums/images/graemlins/smile.gif The guy with the biggest, fanciest, name brand toolbox and the most tools is going to be looked up to by the other mechanics, the shop owners, and the customers. He may or may not actually be the best mechanic in the shop, and
5) those trucks take trade-ins when you want to trade up to better tools or toolboxes; something you won't find in most stores. You probably won't get a lot for your trade-in, but it's better than nothing. And sometimes, you'll get more than you expected. For example, that tool truck can sometimes sell a used Craftsman toolbox for more than Sears gets for a new one just like it simply because he can sell it to a mechanic who will make weekly payments for 10-20 weeks instead of paying outright for it like he'd have to do at Sears. (Yeah, I know Sears has charge accounts, or you can use a credit card, but the tool truck doesn't charge any "interest" - he just sells high to start with /forums/images/graemlins/blush.gif)
Oops, I've rambled on too long. Good luck in your future profession.