I went ahead and bought GSA today. I used the trial and saw really good results but I also made sure to be smart with the setup and how I went about adding my options. I use a pretty big black list for keywords and urls. I set my submissions very low on my tier 1, little bigger on tier 2 etc etc. I keep the pages I post OBL very low, I don't index and I use my own well spun comments, titles and articles to ensure they are all readable. These settings during my trial allowed me to see results a few weeks after when things settled. I also don't mess with pingbacks and trackbacks guestbooks on my first tier and rarely on my second tier.
The point is it's obviously best to put the time into setting up your campaign. You don't build a house on a wobbly weak foundation - you put time in and ensure your foundation is solid. Your campaigns should be the same.