I have had my lipos for about 6 mos.They almost seem like the have more power than before,could just be me.The runtime is the same and I have a lot of cycles through them.It is the best money you will ever spend,the runtime and power is staggering compared to regular batteries.Do it!
I've had my Thunder Power packs for over three years! Well over 300 runs. They just recently all "puffed" with in 3 months of each other (six packs of 2S4P 8000 mAh). I also have two 4S4P TP packs that are almost 4 years old with about 200+ runs that are still in perfect shape.
I sent them back to TP and they are replacing them at 50% off list price.
I would highly recommend LiPos for longevity, and TP for performance and company customer service.
The newer packs have balancers which should make the packs last even longer.