beyourownit, I confess that I've also, on occasion, used a vacuum cleaner to do some cleaning inside my computer and have not experienced problems because of that. But, I've seen enough comments in forums advising it that I never recommend it.
When I've used a vacuum cleaner, I've been careful not to directly touch the motherboard with it. One technique I've used is to use a vacuum in conjunction with a can of compressed air/gas and just use the vacuum to remove dust-filled air generated by the compressed air/gas. That way, the vacuum touches nothing in the computer. Of course, another option would be take the computer outdoors to blow dust out of it.
Other factors might be worth mentioning here, too, such as level of humidity in the air. Also, I think perhaps we should assume that some vacuum cleaners may be more likely to cause static electricity than others. So, again, I've seen enough comments in forums advising using vacuums that I refrain from recommending it.
