This is only a single anecdote but:
I run the IT for a small school in London. I have two very IT-knowledgeable people directly above me - the head and the bursar. Our ADSL provider recently took it upon themselves to chop our business connections, without warning, because "We were using more than an average ADSL home connection". Negotiations were completely fruitless, with the bursar starting out by literally saying the words "How much do we have to pay you to put it back on?" and ending with threatening to take the children out to the playground, and photograph them pointing at a load of laptops, netbooks, etc. showing a 404 page and sending it to the local press.
The ISP were complete idiots, no doubt, and lost a very reliable and well-paying customer for the sake of a few Gb (they also lost all our ordinary phone business because of their stupidity - that's only a dozen lines but it was one hell of a bill each month for the lot). They didn't understand the concept that 450 kids+staff use more bandwidth than a little grandma, and they knew we were a school from day 1 - they did the installation!
We asked for our options and were told that the *only* thing we could do was get another line installed to share the bandwidth across (which we would have to setup!) and that would take two-three weeks to install - in the middle of the exam period for students. In the meantime we would be completely without Internet access because we were limited to only 128Kbps which barely lets us collect email school-wide, let alone do anything practical. They refused to "re-activate" it, or increase our bandwidth allowance no matter what package we signed up to.
If we had to install another line, it might as well be with a more tolerant ISP who understands what "business line" means, so we severed the connection and instructed another ISP to initiate a dual-ADSL installation immediately. That left us with 2-3 weeks in which to cover ourselves for Internet access (when England were still in the World Cup, too, I might add!).
I posited an emergency measure - 3G dongles. I had one of my own that I always carried on me and I had in the past plugged it into our systems as a test device. I knew they worked well enough if we were careful, and I demonstrated it to the head.
Immediately, the bursar whipped down to Argos and bought a shed-load of T-Mobile 3G dongles with 2Gb allowance / month on each (and then they limit you, not charge you). We topped them all up with some cash, plugged them all into our Linux firewall/router, I wrote some scripts to automate things a little (e.g. switch between dongles that had already used up their monthly allowance etc.) and hey-presto - several 2-3Mb connections school-wide that I could load-balance and switch between in order to balance demand, speed, bandwidth usage, top-up-credit, etc. As far as anyone else on the network was concerned things just started working again, Internet-wise.
It cost us about one-tenth of what our up-to-8Mb ADSL package was costing us, it gave us similar speeds, much better upload, greater reliability, and seamless Internet access across the school without having to buy any extra hardware except the dongles (which we've since redeployed to staff for school trips, home VPN access, etc.). It worked perfectly for 2 weeks, then our up-to-24Mbps ADSL came online and we only kept a couple of them plugged into the router for emergencies.
Now consider that this was done by plugging in a handful of cheap 3G consumer dongles into the various USB ports available on a Linux PC that acts as a router/firewall, with some of them basically sandwiched in between two others because of the proximity of the ports. Consider that the room this was in is some way inside the school and had tons of copper running through it (including network cabinets, the phone system, servers, etc). Consider that it was in the middle of a school, filled with staff using mobile phones, in the middle of a London town, surrounded by houses and main roads and just a few hundred yards from the main shopping road.
The dongles didn't even sniff at it - they just got 3G connections each (not maximum theoretical, obviously, but each good enough to use it happily without noticing slow-downs), and worked flawlessly all day and night. We scripted overnight shutdowns for them in order to reduce bandwidth but each morning they came back online like a champ, and ran an entire school sometimes on just one or two when we were initially testing. It felt slow with only one, but nobody complained - they had "usable" Internet that was a damn-sight faster than our limited ADSL. Windows updates, anti-virus updates, web browsing, Java games, Facebook uploads, clipart browsing in Office as an entire class - you name it, it occurred during that time and worked perfectly. I was downloading a new copy of OpenOffice at the time, too.
We *did* ban any streaming of the world cup - we felt that was taking the piss slightly, so instead we streamed matches over the network from a DVB-T stick using VLC. Otherwise, 3G saved our arse. Our other alternatives were literally things like asking the neighbouring houses if we could tap into their wireless or run a cable into their house, or pointing a wifi antenna at a local OpenZone hotspot.
This was obviously only a static setup, but I think that's pretty much a worst-case scenario - a pack of 3G dongles all touching each other, all connecting at the same time, all from "unique" customers, all on the same base-station, all trying to get the maximum out of their connections simultaneously with real, varied traffic, within the borders of Greater London, near main roads, shops, houses, etc. It worked damn well, better than we ever expected, and I'd do it again in a trice if it was necessary.
Oh, the bursar complained because his office is in the next room and *his* own personal 3G dongle (which he used when uploading anything critical) occasionally went from 3G to HSDPA when we did this.
3G works. T-Mobile did a fantastic job, even if we were abusing their services a little. The mobile network worked better than I ever would have imagined. If anyone ever says that 3G is shit, or isn't capable of things like that, it can *only* be under-investment at the mobile carriers end. In our case, everything just worked. Best £20 I ever spent, buying my own 3G dongle.