My review
OP gave me a years free subscription to this service (I would have definitely been a buyer anyway though).
Here is a short review of the service as thanks for the review copy.
The interface is very good to use - its easy to log in online and add signautres and then to copy the BB code or HTML code and add the signature to the forum.
How I use it
I have played around with a few adverts up until now and have found that banners work best (On BHW anyway). I had several different affiliate programs I wanted to promote though, so I tried text signature instead but this doesnt perform nearly as well as banner.
So with sigpool I have now set up 6 different banners, each with different affiliate links, I add a single BB code to my signature space and set the ratio that I want each banner to be displayed.
Sigpool then takes care of rotation and in their web portal I get a nice easy view of each banner along with how many views it has had, how many clicks and the ratio it is displayed.
I have run all of these banners for the last 7 days and found 2 of them have double or triple the CTR than the others so I have now removed the lower CTR ones.
My next step will be to keep just the highest performing affiliate programs and then rotate some different banners from the same programs to get even better CTR.
How else you can use it
If you are selling your signature space then you can offer banners to people on a percentage basis. This means that if you have a good account and want to sell banner its easier to sell to a few people at a lower price (probably wider market) and also you can charge a bit more than you would for the entire space.
If you are a buyer of signature space then you can use the same BB code and give it to several different members, that way you could have 5 signatures occupied but manage banners from all of those spots centrally from sigpool - if you want to change banners you can, split test across all signature spots you can.
Lastly you can also geo-target the banner display, but I haven't tested that yet.
Disclaimer: Although I may seem to be heavily in favour of this service I have no affiliation at all. I was happy to pay for it but OP gave me free copy. I just think its a really good service.