Some really good, valid posts in this thread...
From my own experience,
[b]You CAN earn enough to pay the bills[/b] - but be prepared to put the hours in, including travelling, homework or lesson prep if you teach.
[b]I spend many hours alone in my car[/b] - driving to sessions or gigs which may be miles away can be a lonely business.
[b]Your family DO suffer[/b] - I've had to cancel many family events over the years. NOT 'coz i just HAD to do the gig/session but 'coz the money was too good, or too needed, to turn down. Also the early morning school run is not ideal if you only got home at 4am after a gig.
[b]Money is ALWAYS an issue[/b] - unlike 9-5'ers, you can never be sure where the next paycheck is coming from.
There have been good points made about letting down bandmates, or them letting YOU down. If your saturday night, £400, corporate gig gets cancelled coz your guitard's car broke down, there is a very good chance that money has gone and there's no way for you to get it back.
Don't get me wrong, I love my job, but it's just like any other job.... Sometimes you have to go 'into the office' when you don't want to or work with people you don't get along with. Previous posts have mentioned the lack of sick pay, holiday pay and pension benefits, If I don't work, I don't earn, simple as that.
Turning your hobby into something you HAVE to do is a big step so be sure before you leap.