how many times do you change mono in a season

Once every spring on all the rods or whenever I get a big birds nest and gotta respool again. Have used Trilene XL green for years and have it on all rods,I rarely change for the new stuff. Tried spiderwire and it ate up my guides years ago when it came out. Crap was like a rope anyway and fish saw it from a long way away in clear Lake Erie waters.
 
P-line was nice stuff though.

Started using 2# fluoro on my ultralight this year.  I get it 2/3 full with a "pony" spool and leave it there for ease of casting.  I change all of it out when I can start to see the spool color through the line (because it's getting low), or when I can tell that there's a difference in castability, limpness, or, most often, discoloration.  When I can see the line underwater, the fluoro has lost its main advantage.  This year, I'm on my third pony spool, but should really only be on two.  Fished in some nasty mine drainage that turned my line yellow/orange!

My other rods I dont use nearly as much and the line is much more durable.  Each one gets changed before it's first trip out after the thaw, as well as anytime I can see its getting low or has some other problem.  Usually the 1x per year thing is good enough.

for trout i use #2 & #4 yo zuri hybrid and for bass i use either #6 or #8 yo zuri flourocarbon green color...i used to use trilene but used yo zuri once and now its all i use...it lasts longer and casts better and because its flourocarbon, fish have a harder time seeing it....i change line about once a month..sometimes 3 weeks...usually right after it molds to the reel and castability sucks.....i fish about 3 days a week and the way i look at it, why go out and buy all this fancy gear and awesome rods and reels and then put crap line on it, or leave the same line on for the whole year....line costs what 5-10 bucks?...i'll pay it if it means im not going to lose any fish due to weak line or knicks in the line.....

i use hi vis green or yellow weed whacker cord with a 90 lbs leader n change it every month

I usually change out the set ups that get most use, once per year.  Usually, one rod will get more use than most, and will get changed twice.  Especially if it is being used in the rivers a lot. 
 
I like the Trilene XL in green too, and will likely be my next purchase when my bulk line runs out.  Depending on deals that I find...
 
I got on a copolymer kick.  14lb Breakaway is what I use on my medium duty set ups, the same diameter as 8lb, but almost twice the strength.  I really like it, but not the easiest product to get ahold of.  So, shipping usually makes it about twice the price of other stuff.  Cabela's used to sell it, so combining with other stuff made it much more feasible.
 
I tried the Cabela's 6 lb copolymer line on my ultralight setups.  About the same diameter as 2lb test and would cast like a dream, but that is about all I can say good about it.  Some how breaks with out any type of stress?  I'll just be reelling in, and notice my line has snapped somewhere...  Then have to bring what ever I have casted out, back in by hand.  Junk! 
 
I use 20lb Cabela's Saltstriker Copolymer, and works great though.  About the diameter of most 14lb lines, and assume the strength of 20lb. 
 
 

ORIGINAL: brown_trt

for trout i use #2 & #4 yo zuri hybrid and for bass i use either #6 or #8 yo zuri flourocarbon green color...i used to use trilene but used yo zuri once and now its all i use...it lasts longer and casts better and because its flourocarbon, fish have a harder time seeing it....i change line about once a month..sometimes 3 weeks...usually right after it molds to the reel and castability sucks.....i fish about 3 days a week and the way i look at it, why go out and buy all this fancy gear and awesome rods and reels and then put crap line on it, or leave the same line on for the whole year....line costs what 5-10 bucks?...i'll pay it if it means im not going to lose any fish due to weak line or knicks in the line.....

I change my line this often as well, well worth the extra few bucks. Here is a hint on re spooling...soak your line in room temperature water for 20-30 min b4 you wind it on. It makes the line ten times more limp, and keeps way less memory.

iv heard of soaking never gave it a shot, ill be respooling my noodle rod , have to get the big boat out next week