I have a Quarq and I'm very happy with it. However I have a short-duration dropout issue and I don't know if it's normal among the realm of power meters. Occasionally I get a zero reading on cadence (and hence power) for about 1-3 seconds. I cannot rule out my Garmin 510 as the culprit as I don't have a second spare head unit to test. Do you see such a thing on your power meter? From time to time I read people have dropout issues but I don't know what's the acceptable limit vs. a bad power meter. Since my power meter is on a wireless connection (ANT+) I don't expect 100% reliability all the time.
I have a similar problem with my setup of Powertap hub and 510. Due to previous problems with Garmins crashing, losing rides etc I also ride with a 920xt, and that seems much more reliable ie very few dropouts, missing data from the G3. So that suggests its a 510 issue.
In Golden Cheetah the symptom I look for is zero power, no-zero cadence and the speed repeated exactly, at least 4 times. For most rides I don't care about the dropouts, but for some eg intervals I do, so I created a Google spreadsheet to look for and fix the dropouts by simple interpolation. NB I used the Google Sheets because it can do nested boolean. Dunno about other spreadsheets, but I know LibreOffice doesn't as far as I can tell.
If you copy and paste from GC you get the following columns
Data Dist Pwr Cad HR Speed Alt Lat Long Slope Temp
so with these columns the checker which I put in column N is
=IF(AND(F7=F6, F6=F5,F5=F4,C7=0, D7<>0),"Fix","OK")
and then I made a template to interpolate depending on if missing 3 4 or 5 seconds of data. The format is
This works for a 3s dropout, you can adjust for longer dropouts.