Having tried the trial this time last year, GSA SER was on my list of tools to buy but never got round to it - I was a sucker for Senuke XCR and my fancy templates that could rank sites within a few weeks. I've now stopped using XCR almost completely. Retired wikibomber, sbbomber, IMSlave, and stopped buying links, press release syndication services and finally, I've ditched DBC, as it was draining cash like mad. I've saved around £300pm from captchas, high PR manual link buying and binned 4 of the 5 VPSs I had.
I have many clients and lots of my own sites, and have been running various test domains with SER to find out what works in what order, with what settings etc etc.
I am seeing good results from churn and burn sites, ranking for medium competition keywords within 10 days (lead gen for national car sales related kws). I am seeing horrendous results with websites on WordPress across many different niches and different hosting accounts.
I'm seeing amazing results for very difficult niches, (finance/loans) in the UK, but for the same keywords in the US, the results are terrible.
I know this will be down to the recent updates and not SER/my settings etc and previous link-building, but it's weird to see and needs lots of more testing and tweaking to get right. I know that not all niches respond to the same link-building.
After only a month with SER, I'm already planning on scaling it up by replicating my VPS set up and buying more SER licenses. I'm very impressed despite my SEO buddies thinking that users of SER will be penalised in some way by Google. I can't see that happening yet, it didn't happen with XCR, as long as you created your own web 2.0 network, changed templates and spun the content/titles very carefully.
Overall, I'm very happy with SER and would recommend it, however, if there is a way that Google can decipher the way and 'style' that SER works and penalises the site(s) that are being promoted/boosted in the SERPs then I would hope that people that own an SER license are careful and don't ruin it for the rest of us.