3) Your ISP. A biggy!
I used to be with VISPA, on a fixed 2M speed package - and I got 2M.
VISPA are considered a 'good' ISP, in as much that they clearly state what your download limit is. If you go over it, you pay extra, simple as
There tech support is also UK based and good at fixing things (generally).
Other ISPs - are not so great
Many run overseas tech support, who do little more than read from scripts and end up telling your to reboot and run a virus scan - not much help when your speed has dropped from 6M to 1M overnight
Others will smack you big time if you step over the download limit - although they won't tell you what the limit is... Usually only happens if you're big into newsgroup downloads.
But if you do step over, you can suddenly find yourself on dial up speeds