hello fattire, its interesting that you raise this point as I was intending to raise a similar topic myself.
I do lots of riding with mates etc, but find that for the most part they are not really into long/really hilly/challenging terrain as I am. this means that for the most part my "proper" rides are solo.
this weekend I did 3.5hrs on saturday, and 3hrs on Monday, nearly all off road. On Saturday because the sun was shining, I saw a few walkers and the odd landrover. On Monday, because it was hammering down rain, I saw next to no-one, just three farmers to be exact (different places, they don;t really hang out in clusters!)
Anyway. point is, although this is only the cotswolds, a lot of the trails are lightly used so if I injure myself I cannot rely on someone else to come along to pick up the debris. couple that with the fact that i live alone and the possibility, at least in theory that i could spend all night in a ditch is a real one. this has only recently occurred to me.
As a result, I've been making sure in the last couple of weeks to ensure than someone knows where I am going, wear one of my lovely dayglo tops and check in when I get back. I of course carry a range of spares and a mobile, but mobiles cannot be relied upon as one of the other respondents has already mentioned.
of course, there is a danger of spoiling the thrill of being alone in the middle of such great surroundings with the thought that something could go wrong, and i won't give up going out on my own, but it takes 10mins for me to ring someone and ask them to check in with me later, and could be worth every second if the worst happens.
Anyway, keep up the trips I say, better to die on the trail than staring out the window wishing I was out there. I could, afterall, fall down the stairs at home with similar results, No passers-by would find me there either!