Pffft, I am Level 25 and have 20 normal wins. Yep, yep.
As the only hardcore bot player, here are my thoughts/suggestions:
*)Bot games are better than their reputation. The goal is not to win, it's to completely dominate. Bots give you a ton of oportunities practicing how to secure a kill. If you don't get good farm vs bots, you also need to practise this more.
*)Easy bot games are great for trying out new chars. No matter how bad, you can't loose it for the team. Some ranked players say that's what normal is for, I disagree.
*)Medium bot games are unfair. I am not certain of the income mechanics but basically, if your teams go even you will loose by minute 30. Unlees constantly killed bots in medium will just outitemise you hard and then win from pure damage and resiliance.
There are virtually no comebacks here unless your team suddenly shows it's really ace in defense.
*)Bot teamwork is actually decent and often better than that of low level players. I am not kidding.
*)Bot games don't require wards since bots use no brush. This leads to bad warding habits in normals.
*)Bots are terrible at zoning defense. Their offense is okay for the most but they do take damage like they want it.
You can learn a lot of stuff in bot games if you set your goals right.
Though that one match I had recently, my normal win no 20... couldn't have had that against bots. Will post a report and replay this eve. All I will say is, this match is almost instructional. Never give up, never surrender ;-)
Bots teach people to be reckless, take tons of damage to creeps, and to hang around with 1/10th health. I started LoL with friends who avoided PvP matches for bots. So I ended up like up in the high 20s with 20-30TT wins and only a few on SR. I didn't know diddly about how people tend to play pokes, or baiting or any of that jazz.
Bots don't play like soloQ. Even the streamed rank matches don't play like soloQ. I find its hard to even follow a build guide 1:1 since most of them are based around the kind of teamwork you won't be seeing. The only thing that seems to help is actual experience, hellish as it can be.
I think custom games with bots are better practice. With the AI's tendency to get stuck and other silly stuff, you find yourself as disadvantages that can be a bit more of a more a challenge then the usual co-op steamroll.