To follow up peoples points on sharpening - doesn't matter how long the chain is. Little and often is best (and quickest). Don't carry on if it feels it's getting blunt, The more you carry one the more blunt each tooth gets and the longer its gonna take to sharpen.
And prep of the wood is the most important. Don't cut dirty wood, used a strong brush to clean out the grit in the bark. Time spent on this is easier than time spend sharpening.
Finally, don't neglect the depth gauge part of the chain when sharpening. This is the rounded protrusion in front of the tooth. it stops the tooth being too aggressive and ripping into the wood. Most chainsaw stores will sell a depth gauge checker for these. Lie the tool over the chain on the bar and see if the depth gauge on the chain stick up above it. If so a few strokes of a flat file will bring it down and remember to round off the profile.
Because the teeth on chainsaws angle down as the get shorter, if you leave the depth gauges untouched, the tooth will gradually take of thinner shavings and take longer to cut anything. Don't take them too low though, it makes the cut too aggressive and you're more likely to get kickback.
Sorry if I'm preaching to the converted, but a badly sharpened chainsaw is one of my pet hates
