do your therapy as prescribed and you will be good as new!
for sure.
But don't over do it!
I have a buddy who had both knees done at the same time. He thought if he did more therapy than they wanted he would recover faster, better, stronger.
WRONG!
He now uses a walker!
Good luck... 
Excellent point. I will be getting the second knee done... at some point in the near future. The left one is far, far worse than the right one (blew it out big time a few years ago). So, I'll be having to keep a limit on it anyway, at least in terms of anything that is doing bilateral strengthening and toning.
Ok so I'm gonna be a little confrontational here...
Your friend is NOT using a walker BECAUSE of how aggressively he did his rehab. When you get out of surgery, hours later the methyl methacrylate is set. The tibial plateau is as solid as it will ever be. The femoral condyle has some healing to do, but it would take serious trauma to dislodge it.
Most problems people have with joint replacements relate to the implant not having been set at the correct angle (that's where an experienced Ortho comes in and why getting by with the least expensive guy isn't a good idea) or infection (cleanliness and dryness are important). Bilateral replacements have a higher redo rate than sequential unilaterals. It is unclear why, but may be related to asymmetric rehab (we tend to rehab our dominant leg faster/better).
Chris, do the "pre-hab" that they recommend. The stronger you are before hand, the better your post op rehab will be. TALK to your PT and let them know EXACTLY what you expect out of the finished product. Do the rehab as prescribed. When you meet with the PT for sessions tell them exactly what you've been doing at home. If they think it's excessive or dangerous, they will tell you.
That said, USUALLY pain stops people from working the replacement leg past where they should.
