I've put about 3k miles on my '01 KLR250 and the farthest that I've been able to ride the bike is 100 miles. Not because I run out of gas, but because my butt runs out of feeling (actually, it hurts!). Right around 65 miles, I start getting a case of "Monkey Butt" and by the time I hit the 80 mile range I'm squirmin' and looking for a chance to stop and lot and "shake things down".
I guess that's why I've only got 3k miles on the bike: 100 miles x 30 rides...

Be aware of this fact before buying one!

 

I had that problem on my atv but not yet on my bike.When i ride i use some MSR padded shorts with the chamois where it counts.Another option for you is this....I did it to my atv and it is awesome.Get a "pro-pad" gel insert.They are available in tons of sizes and shapes and then remove your seat cover and trim away "X" amount of seat foam to compensate for the addition of the gel pad....then recover it.I did this on my atv as 100+ miles off road will where holes in your rear end and it worked very well.
When it's hot out where the shorts and also dump a liberal amount of gold bond powder (green bottle) down the crack in the back...I know........believe me it works and works well.I have tried everything possible to remedy this problem as my atv was really killing me....the bike on the street seems real easy on me as it's so smooth on the road.

 

I went on a 150 mile ride last summer, and man that was rough on a seat that's not really meant to "sit" on. One thing I noticed is that if you stand and ride off and on every 10 to 15 minutes it really helps.