How often does everyone clean or service their reels? Is it a good idea to clean and re-oil/lube a brand new reel?

I do mine at the end of the season, unless I have really used the tar out of one.  I can only comment on Shimano reels, which are usually over oiled and greased out of the box.  I am less concerned about the grease, but I always remove the spool bearing, clean them well and oil with a tiny drop of oil.  I use Yellow Rocket Fuel, but there are other quality bearing oils out there.  It does make a difference in the bearing performance (much faster). 

Really it depends upon how much you use them and how concerned you are about maximum or optimal performance. I have a few reels that may get fished only five or less times a year and they may get professionally serviced every two years. The reels that see normal to heavy use get professionally serviced once a year. If a reel has a problem that I cannot fix I will send it in as well.

If you are capable of servicing a reel and have the means and supplies to do so it wouldn't hurt to flush and re-lube the bearings on a new reel right away and service the reel a time or two throughout the year.

Always have the schematic with you and take pictures as well. Otherwise send it to a place like DVT ... plus he offers members a 10% discount.