Speaking as a retailer...
We didn't notice a big surge in "Nemo-mania" until the DVD came out. Sure, lots of people point out Nemo and Dory (2 of each) in our display... they were there long before the movie. But I didn't have anybody come in "just" to buy a tank and a Nemo-fish... And if they had, I would have sold them a book first.

Most got turned off when I told them how much it would cost to buy a tank, filter, skimmer, rock, sand... too much money for a "Nemo"... how about a nice Betta splendens and a little Betta Kit... all that and a book about its care for around $20. If you like the hobby after that, come see me and we'll discuss upgrades
Folks who are willing to drop hundreds or thousands on a setup of some description, but balk about $35 on a book or a test kit, SCARE ME
I *have* had a surge in existing tank-owners/hobbyist want to add a Nemo-fish (new name for common clown...

) or a "Dory Fish"

to their current setup, and if it's appropriate, I oblige. If it's not, I say so too. But that's just me.
I think the MEDIA made a lot of hype. When the movie came out I read stories about kids flushing their parents' fishes down the toilet... I even read about some 10-year-old flushing his father's Harlequin Tuskfish, right out of the 150 g reef. Show me an ADULT that can catch a tusk in a 150 without ripping it apart....nevermind a child. Sorry, but just not believable. I think a lot of the "news" was fabrication.
Oh sure, some people probably went out and went overboard, but I really don't think it was on the scale that some would have you believe. Like I said, we just didn't see anything like that. Sure every person that comes through the store associates the fishes with the characters, but that doesn't mean anything.
When we wrote our business plan, I found studies that showed that the aquarium hobby was second only to photography, in popularity/growth.
Here's some stuff I found in my research...some might surprise you...
Marine Aquarist Profile:
Age
The typical American saltwater aquarium hobbyist is 40 years old. (International Survey of the Reef Aquarium Hobby, 1997). The majority seem to range between 20-50 years old. (APPMA 1998, and International Survey of the Reef Aquarium Hobby, 1997)
Gender:
Although there's controversy on this data, we can assume that most hobbyists are male. Data from the APPMA indicates 40 % are males and 57% are females, while the survey from the ISRAH found 91% are males. (Envorinmental Media Services: American Marine Aquarist Profile)
Household Income:
The average household income fror hobbyists is $47,000. Most hobbyists make more than $35,000 a year and 36% make more than $50,000 (ISRAH, 1997)
Children:
Most (62%) have no children (ISRAH, 1997)
Time as Marine Aquarists
Hobbyists usually maintain a
marine aquarium for at least 5 years (ISRAH, 1997 and APPMA, 1998)
And here's one that really surprised me...
Contact with their Community:
The majority of hobbyists (71%) do not belong to aquarium clubs. (APPMA, 1998)
I've got lots of other interesting factoids gleaned during the writing of the business plan too... but thought those were most relevant to the question posed.
We researched where hobbyists live (most on the East Coast), followed by Pacific region), most in large cities...
It's interesting, for me, after doing all that research and seeing all those numbers, to compare them with my actual market/customers. IMO the information is reasonably accurate. I do think there are more women in the hobby than some might think, I strongly dispute the 91% male numbers that the ISRAH study found, yet I don't think that 40/57 is accurate either. I think most are male, but it's closer to perhaps 60/40 in my unscientific observation.
I think the surge in interest stems from huge advances in technology and knowledge in how to keep creatures.
I do remember metal-framed aquariums -- of course nobody succeeded with marines in these... we now know that. The glass aquarium enabled long term success with fishes, and I'm sure there was a lot of trial-and-error with other creatures too.
It's amazing now, even in the short time (17 years) that I've been in the hobby, I've seen things improve. We used to leave live corals in the shop for "rich people" to buy, because we knew they would die... now even newbie hobbyists can have success with corals. Advanced hobbyists are discovering secrets to keeping tricky animals... every day the knowledge pool gets bigger, and tools such as the Internet are making the sharing an distribution of that knowledge INSTANT.
The biggest threat to the hobby is long term sustainability. Destructive collection practices still go on, and aren't discouraged on a large scale. Unless the industry reforms from within, the potential for its decline is serious. As hobbyists, you have a lot of power to effect change, by educating yourselves and demanding ethically and sustainably caught livestock, supporting some captive propagation (but IMO captive stock should not exclusively replace wild caught). Be aware, ask questions and push for positive change.
Hope some of this information is helpful
Jenn