Reading Thad's thoughts on Hanna and Barbera (I know he makes fun of me for posting about what I've just seen on TV, but he forgets that I just as often post about what I've just read on someone else's blog!), I was reminded that the success of Tom and Jerry series had a sort of ripple effect on the cartoon industry. I can't prove this, but it seems to me that a lot of the other cartoon studios changed their approach and even certain elements of their production process based on the huge popularity and prestige (all those Oscars) of the cat and mouse series.
For one thing, I think Tom and Jerry helped establish the idea that one director, or team of directors, should be exclusive to a particular series. Obviously there had been other characters who were handled exclusively by one director, either because the studio only had one director or because only one director wanted to use him (nobody else was fighting to borrow Sniffles from Chuck Jones). But in general it seems like characters belonged more to studios than to particular units within a studio. At Warners, the star characters the studio came up with up to 1940 were shared by all the directors at the studio: each director was expected to make cartoons with Porky, Daffy and Bugs. (Even if, as in the case of Frank Tashlin and Porky, they hated that character.) Fred Quimby's decision to assign Hanna-Barbera exclusively to Tom and Jerry was different. Normally if a studio was going to give a big push to a character or series, they'd assign the series to all the directors; perhaps because MGM's other unit was headed by Tex Avery, who wasn't right for T&J and who Quimby didn't really trust anyway, the idea was to make the push for these characters by freeing up their creators to focus completely on that series.
It worked, obviously, and from that point on, cartoon studios were clearly more aware of the advantages of having a character handled by one unit exclusively. What's more, there was increased pressure on cartoon directors to come up with new star characters; that was a part of their job in a way that it hadn't been earlier, when character development was piecemeal and no one unit really "created" Bugs or Porky. At Warners, every unit started scrambling to come up with its own exclusive characters. Bob Clampett left just as the T&J craze was starting to take hold, but he was obviously thinking about the need to start up his own series: he was apparently getting ready to do more with Tweety (according to some accounts including his own -- which can't necessarily be trusted -- he'd already decided that Tweety should be teamed up with Sylvester), and he was doing pre-production on "The Goofy Gophers" (which was directed by Art Davis after Clampett left), an obvious attempt at a "pilot" cartoon for a potential T&J-ish series, albeit with a Clampett twist. Chuck Jones, Friz Freleng and Bob McKimson were all looking around for series ideas. Warners also followed the T&J lead when it came to submitting and promoting cartoons for Oscar consideration: the first three theatrical WB cartoons to win Oscars were all "series pilots" that took previously-existing characters and re-launched them as the stars of rigidly-formatted T&J type series. ("Tweety Pie," "For Scent-imental Reasons," and "Speedy Gonzales.") Except for the Speedy Gonzales series, which was shared between two units because it was a McKimson character developed by Freleng, there wasn't really much sharing of characters between units.
The advantage of this approach was that a character looked the same in all his cartoons, and all his cartoons shared the same approach. The disadvantage is that without multi-unit work on a character, they tended to be a little one-dimensional. Tom and especially Jerry are not very interesting characters to me; Avery's MGM characters, to the extent that he could come up with any, are like parodies of one-dimensional cartoon characters (literally so in the case of Screwy Squirrel). The single-unit, post-1945 WB characters don't have the depth or variety of Bugs, Daffy, Porky and Sylvester; you couldn't do as many things with them. Hanna-Barbera and Quimby sort of reduced cartoon-making to its essence: have one or two characters, have a formula, have a good unit working on that series. (Again, this had been done before -- Popeye, for example -- but almost by accident. And Popeye cartoons had more variety in terms of setting and plot.) But that approach helped make post-1945 cartoon-making a bit more predictable than it had been.
The other thing T&J may have done was to help increase the violence quotient in postwar cartoons. Hanna-Barbera, of course, sort of learned cartoon violence from Tex Avery; but Avery's cartoons weren't very influential at the time (MGM didn't promote them for Oscars and Avery's characters, if you could call them that, didn't hit it big), not compared to T&J. The extreme, outrageous violence in the T&J cartoons helped change the perception of how violent a cartoon could get without alienating the audience or losing Oscar-worthy respectability. (Again, the violence in Popeye cartoons is a bit different, as a lot of it is really just broad slapstick fistfighting that you could find in live-action comedies too.) And suddenly every cartoon studio was amping up the violence and pain. Even Warners. If you look at Warners cartoons from before 1945, what's surprising is how little actual violence there is. There are some violent gags, of course, anvils and mallets and such, but a gag is just as likely to have a non-violent punchline as a violent one, and very often, gags that seem like they're building up to violence are not building up to anything of the kind. (Two examples: in "The Big Snooze," Elmer walks off a cliff, looks down, sees that he's walking on air -- and rushes back to solid ground without falling. And in "The Unruly Hare," the entire last section of the cartoon involves Elmer and Bugs handing off a lit stick of dynamite to each other -- but they get rid of the dynamite before it explodes, and instead of blowing Elmer up it automatically lays the train tracks.) By the late '40s, every other gag in every studio's cartoon involves somebody being blown up or falling from a great height, and you'll almost never see a stick of TNT or an anvil without the violent payoff. Hanna-Barbera sort of rewrote the rules of how much damage you could inflict on characters' bodies and how much of a cartoon could be devoted to cartoony violence.