To purchase pressure washer or not?

A few people have been buying pressure washers recently, and I'm wondering if they're worth getting.
The main jobs would be for washing the cars (Mine takes ages as it's a people carrier, so anything that helps would be good), cleaning the drive, paths, etc (They get a bit grubby as I do my car fixes on the drive, so they end up with coolant stains, oil patches, etc) so not a huge number of tasks but I'd want it to work well for these jobs.

Therefore looking at the type of pressure washer is important. Recently I've seen deals for them such as the Bosch AQT 33-11 which keeps going on offer down to around £50 which is a good value price. However as most deals, the devil is in the detail and looking closely you need to check a few specifications on them.
Here's what I've found out:
Power output - The energy consumed by the washer, in rough terms the higher the wattage the more power it will draw and vaguely the more powerful the motor will be.
Flow rate - Probably the key, this is the amount of liquid it will transfer within a specific time. This is normally in litres per hour, so the higher the value the higher pressure/volume of liquid is being pushed.
Mains fed/Tank fed - To allow you to run it from a water butt or tank, a handy option if you've got additional water storage and don't want to use the mains-fed water.

So based on that, you can start to make a choice on washers. The cheapo Bosch AQT 33-11 is predictably not that great. From the few that I've seen doing the rounds I've put the following together:

Bosch AQT 33-11 approx £50, 110bar, 1300watt, 330l/hr.
Nilfisk C120 approx £100, 120bar, 1400watt, 440l/hr.
Bosch AQT 35-10 approx £99, 120bar, 1500watt, 350l/hr.
Karcher K2 classic approx £120, 110bar, 1400watt, 360l/hr.
Karcher K4 approx £150, 140bar, 1800watt, 420l/hr.

So pricing varies by £100 and there isn't a huge difference in the pressure or water rates, although the £50 Bosch shows it really is underpowered compared to the rest.

So all in all, I'm still unsure about buying one at the moment as prices vary a lot and there isn't a huge difference for the money from what I can tell.

Oh and when you can get your car washed for £5 to a decent standard, that gives me 20 washes and 0 effort relating to the £100 pressure washer!

Tell me what you think, especially if you have one and like/hate it.