Here we are - day 10! As this is going to be a tad long I'll break it into a couple entries. As this first entry will be under the 2nd, I'll do the results/thoughts first.
To me, this was a success. I went from less than 300 followers to over 1900 in 10 days. The actual effort put forth was minimal. I hardly said more than hello each day and spent maybe 1/2 an hour on tweepi cleaning out non-follow backs and adding new followers.
There were a few issues I wasn't aware of or expecting. The 1000 following cap per day, the 2000 following overall cap - neither of these did I know about until I started this experiment. Due to that, I had to switch from a daily tweepi interaction to a bi-daily, to give the new followings more time to follow back. I don't think this really interrupted the stats, but I wish I had started with bi-daily just to be more consistent.
Ultimately, I think this tweepi site benefits anyone willing to use it. I can see the argument that these followers of mine don't know anything about me, it wasn't a natural addition, they simply are just following back to be nice. I agree, they are being nice. However, it's that kind of attitude that also gets things retweeted - for the sake of being nice. Now, all those people who retweeted my sales or reviews are catching the eyes of their followers and perhaps retweeting it themselves. This snowball effect may not happen at all, but there is a much better chance it will with 1900 followers vs 300.