Just thought I'd post a message with my story which hopefully can help people suffering with patellar tendonitis/jumper's knee.
I ignored the tell-tale ache below my knee cap for months and finally while playing football the pain became intense and I could hardly walk.
I tried physio and anti-inflammatories for many months - about a year, in fact - but the slightest thing would cause it to flare up again.
Like others above I've found rest, then stretching and eccentric exercise, much more effective.
But also, and this may sound stupid, due to the type of pain and ache you get with tendonitis, I often rubbed and massaged and fiddled with the tender part of my knee cap thinking it would help, which I now think actually was making it much more inflamed.
I stopped myself from rubbing or touching the tender part of my knee and my condition vastly improved, quickly.
I am now pain free and have been sprinting and running without any flare ups for about 5 months.
Tendon straps may help you last a bit longer before the pain kicks in, but they don't solve the problem.