I perk it mostly out for roleplay reasons, but I don't view it as particularly useful.
The only perk I think is actually useful is Merchant, since it increases the inventory of merchants and allows you to get some rare items that are pretty much otherwise unavailable.
Edit: I think Alteration has some useful perks, like the magic resistance and Atronach, but the magic school's spell selection is lacking.
I perk it for RP and fun.
I was REALLY worried when I first got that last perk for adding 1,000g to all vendors - fearing I just wasted a limited point. Man, I can't tell you how convenient that is! It actually even converted most of those useless inkeeers and fruit vendors into viable loot-dumps!

So nice to see them with 1,100g instead of 100g! And seeing the fences with 5k instead of 4k helps too for higher ticket items to sell!
((Note, not ALL of the vendors get 1k for some reason. The food vendor in Riften, Greymane's wife in Whiterun and a few select inkeepers don't get the boost for some buggy reason. >_<))