i really wish that they would make this perk useful because i thought i would get an income from them or something. disappointed when i wasted all of those skill points for nothing
Before I answer this - please keep in mind I'm a PS3 owner.
I've never regretted that ONCE where you can invest in a shop!
First and foremost - it MUST be mentioned that if you invest in the Riverwood Trader, his pool increases to 10,000g instead of 500g like the others. Some SAY it's a bug - but that's a pretty damn specific bug if it is! (I discovered it by accident, btw!

)
Secondly, you'll be loving it when you're selling high-cost items. Once I got the (spoilers for Stones of Barenzia incoming!) Prowler's Profit bonus, I started manufacturing jewelry for profit instead of keeping/upgrading all that heavy junk to sell. Now, I just vendor everything when I get them at the riverwood trader/fences - and then I have the PERFECT amount to sell Diamond necklaces (1,200g) to the vendors (now at 1,500g after investment!).
And when you take the FINAL perk for adding 1,000g to all vendors... you bet you'll be rolling in gold!

...what's that? You all think gold is useless? Meh... you have no imagination and no idea of fun! Gold lets me "store" things in other people. I don't have to keep stockpiles of enchanting gems anymore... I can just buy them when I want them. I don't need to constantly go on mineral farming excursions, since I can just buy the bars right from the vendors and it saves me a disgusting amount of time.

And it's especially cool to have gold - since I may, one day, get DLC content to spend all that glorious gold on!

EDIT: And FYI - investing in peoples businesses count towards helping them, which is a pre-req you need for being a Thane in the provinces, and elevates your friendship level with them - which is good for looting some nice items (if you're not a thief, that is!

).
And, sometimes, investing can lead to fun reactions. The Hag's Cure, for example - she's just really greedy and laughs at you when you invest in her. The BEST result, however, is at Radiant Raiment's in Solitude. Remember those REALLY stuck-up sisters who snub their noses at you every time you talk to them? Invest in them... and they're dialog and attitude towards you TOTALLY changes and they now treat you like your their best friend!
