3 Usb Modem

I got one of these USB modem dongle thingies a couple of months ago. I was generally pleased with it, but not now. To explain what it is: you plug it in to a USB port on your computers and, provided you can get a decent mobile signal, you can surf the internet. (Look at the website link for picture.)
I got a 3GB model on an 18-​month contract for £15 a month, and so far I’m using less than a fifth of my allowance. Most weekdays I just use it for maybe an hour a day (looking at news sites, editing Wikipedia, doing emails, reading forums etc. is what I do mostly).
It’s especially useful when commuting on the train as I can use up the dead time more effectively and also save on dead trees by not buying so many newspapers. What I save on newspapers almost covers the cost.
Shortcomings: it only works with Windows and Macs. Sometimes you can’t seem to get a strong enough signal (even in places where you can have a faultless phone conversation) to use, and sometimes it just slows up for no apparent reason. In fact, during the last couple of days when I’ve been stuck at home, the bandwidth continually seizes up to the extent that for half an hour at a time it’s unusable (taking 10 minutes to load Google, for example).
One thing I can’t do any more is spend five hours on a Saturday morning watching YouTube videos (uses a lot of bandwidth) but maybe that’s a good thing. And the BBC’s iPlayer is out of the question.