I signed up last year sometime, but never got around to registering my cards until a few months ago (lost a lot that I could have been earning on last year's Christmas gifts that I purchased at TRU). I just mentioned UPromise in a different thread.
Before I buy anything online, I check eBates first (http://www.ebates.com/
[email protected] &refpageid=1 ) since I like the "cold, hard cash" upfront. :-) Then I try MyPoints, and finally I'll use UPromise if I can't find the store anywhere else. UPromise is down this very momment, so I can't tell you how much is in my account. I also registered my parents grocery store card under our account (since I can never get my mother to set up her own account). You can also download a program to your computer that pops up a reminder box whenever you go shopping at a site that belongs to UPromise (Lands' End, Martha Stewart, etc.) and you didn't get there through UPromise's link. The other sites (eBates and Mypoints) have these too, but you can only have one installed on your computer at a time.
I don't believe the money is "invested" until you set up a 529 plan. I haven't looked into this part yet (and I can't get DH to sit down and figure it out for me). I think I signed up because it was free and I could earn MyPoints for doing it. Eventually I went back and registered our cards.
Edited to add this:
How do I know my money is safe at Upromise?
The money in your secure Upromise account is yours, available to you at any time, and held in custody by Upromise Investments, a registered broker-dealer with the SEC and a member of the NASD. Upromise Investments is also a member of the Securities Investor Protection Corporation (SIPC), which protects securities customers of its members up to $500,000 (including $100,000 for claims for cash).
From https://secure2.upromise.com/content/faq/aboutus_1.html#22x