Interesting debate, i'd echo what Inkey said in his first post tbh. I'd probably not reply but sometimes i think it's really important that people see other's opinions on this, especially in this case those who just say 'no, its illegal, hang anyone that uses it'. Have open minds folks, open minds.
There's a few questions here, firstly - legalisation.. Personally, i'm all for legalising it, regulating it, controlling flow, taxing it, monitoring it heavily and adjusting regulation accordingly. Do i trust the govt to do this effectively? no, but can we continue in society to not advance because we have no faith in the govt? guess not.
Some reasons to legalise it, imo:
+massive tax income
+legalised recreational use would promote safer (weed) variants, rather than the less (hardcore wtf my brain is melting skunk). Frankly, it's just much more fun, which is why people do it.
+might help prevent the use as a gateway drug to further, more dangerous illegal stuff. If anyone has ever had a 'dealer' the pretty heavy skunk is usually the most 'lightweight' think they'll try and sell you. Nothing about Marijuana makes you want to sit in a slum chewing crack rocks, it's the connection to the darker side of drug underworld that might link you to it's availability and becoming part of the scene.
+education on it's use, dangers, risk and consequences.
+crime rate reduction.. MASSIVELY.
+less money being pumped into the criminal world
Secondly - medical? Yep, no reason why not.
Third question here - should this guy, aged 18 or whatever be using it regularly? no - scientific evidence has proved it WILL (and probably already has) heavily affect certain brain functions, including memory. I have a friend with similar insomnia problems, the prescribed stuff doesn't work at all - so i can understand why you're doing this - but i'd (if i were you) make as much effort as possible to find alternatives for the next few years at least.
Endless debate really. The recent Channel 4 program was very good, though clearly had an agenda (warning people about skunk vs standard cannabis). For the US audience, get a browser proxy and connect via the UK: http://www.channel4.com/programmes/drugs-live/on-demand
Currently you've got people like (no offence) half of this forum who think it's bad regardless of what anyone says (including the worlds top scientists), just because it's illegal. This means their kids grow up having no exposure to it and no idea about the risks/dangers when young, and frankly they wont ever discuss with their parents - but i guarantee they'll get hold of it, and it wont be the good (read: safe) stuff. Then again these people could probably do with a bit of worldly experience, travel the planet and see how the other half live - but chances are if you're in a position to be driving a Z4 you're probably past that life phase so maybe it's too late for you. Thankfully - my generation is coming along (fair, liberal, not god fearing, more accepting and green aware!), and we're gonna fix this stuff for the(our) future

Adios!
All my opinion, so don't take this as an attack on yours - it's great to have healthy debate, maybe some people (myself included) will learn something from having a discussion.