As global economic conditions get chillier (already things look much worse than the early 90s), it is becoming increasingly difficult to find early stage venture funding. If you're in a job, are you really going to leap out into the dark (illuminated only by your BizSpark sparkler) and start up a new business?
Possibly, possibly not. What a lot of software folks can do is to start burning the midnight oil to create their new technology, so that there is something tangible to invest in.
If you go down that route, then you need to be very careful that you are not falling foul of your current contract of employment. At the very least, you need to make sure that you don't use any of your employer's resources (PCs, equipment, time, space, heat, oxygen) to do the job. And if they have first right of refusal on anything extra-curricular, make sure you get that waiver in writing. It doesn't matter how many verbal assurances you get, if you do anything even slightly successful you'll find that they were never said.
Which brings me to a sideline of my own. I was down in London last week, and caught up with some friends: Brian Randell, Ian Griffiths, and Felix Corke. Brian has cooked up a project which sounds very interesting - a data visualization problem in WPF. I'll leave it to Brian to explain the background, but it should be interesting, and result in something pretty useful (at least two of us already have something in mind for it when it is done).