These seem to disagree... (and apparently breaking up the scar tissue can be very painful).
http://www.breastcancer.org/bey_tre_recon_Implnt.html
Scar tissue
Once a breast implant is in place, scar tissue forms all around it, forming what's called a tissue capsule. Most of the time, these tissue capsules are soft-to-firm, and unnoticeable. However, less than 15% of the time, a hard capsule forms that can be painful and distort the breast. In these cases, a surgeon can break up the scar tissue and, if necessary, replace the implant.
If you have radiation therapy to the breast area, the risk of scar tissue and hardening around the breast implant increases to 4050%.
Massage and exercises may reduce the risk of forming a hard capsule (with or without radiation). You can ask your surgeon to show you how to massage the implant and the area around it, firmly but gently.
Shifting, leaking
An implant has a small risk of riding up the chest, so you may have to massage it down into place.
Occasionally, implants leak fluid. The chance of your breast implant leaking increases over time. Most implants that have been in place for 1015 years have some leakage, but it's usually insignificant.
You may be able to tell if your implant leaks, because your breast may get smaller.
A small leak of a saline implant can't be detected. Leaking saline is harmless.
Even a small leak of a silicone implant can show up on an MRI (magnetic resonance imaging) scan, or sometimes on a regular X-ray. While this isn't necessarily dangerous, it can lead to complications that you'd rather avoid. If you suspect a silicone implant is leaking, have it checked and, if necessary, replaced.
http://www.breasthealth.com.au/careafter/implants.html
What are the disadvantages of breast reconstruction using an implant?
The disadvantages of having a breast reconstruction using an implant (over other types of reconstruction) include:
The breast may not be as lifelike or natural as other types of breast reconstruction
In some cases, a capsule of thick scar tissue forms around the implant this can make the breast feel firm and uncomfortable
The implant may have to be replaced at a later time
You may get an infection and the implant may need to be removed
If you have radiotherapy after having an implant, there is a risk that the tissue around the implant could become harder.