Every server is different, and as we have several, performance can obviously vary. Nevertheless, most, if not all, servers have had high uptime within our guarantee for the past year. You can't always expect low server load while paying a few dollars per month on a shared/reseller account, so keep in mind that your expectations need to be reasonable. On the other hand, we do pride ourselves with strict anti-overselling policies and low sites-per-server ratio, which other hosts do not offer at all.
In general, if there is slow performance, it is an isolated incident caused by abuse, sites exceeding memory/CPU limits or combination of other factors. Thus, we encourage customers to report them to our support department, but to generalize without long-term proof or evidence on a public forum is neither an effective nor proper way to address your concerns if they are legitimate.