Guassian Blur and Sharpen are near enough necessities, but not really dramatic filters. Don't use Twirl etc.
I would have to agree, Gaussian Blurr is one of my top used filters. Filter tricks are handy, and the first thing you should learn next to brushing but they really are more used for manipulations ect ... like turning photos to cartoon style scteches ect .... Used in the right manner though can be very effective.
Gaussian blur, sharpen, displace, wawe and rarely ripple. I use topaz vivacity filters for finishing touches, they're good