Frankly, the write filter story is **bleep**. Those flashdrives are just mini PCI-e solid state drives. We even managed to swap one out for a bigger one for testing purposes a while ago.
We have 110 T520's with WES7 running for 2 years now. They all have their write filter turned off because we couldn't get single sign on working for Citrix, the login webpage needs a cookie to perform single sign on and that cookie gets altered after every login. There for, the write filter would prevent people from logging in.
My home pc has an 128GB Crucial M4 SSD in it, obviously no write filter on it, has been running flawlessly for almost 5 years now.
Yes, any flashdrive deteriorates over time (guess what, so do traditional harddisk drives), but I see some people on the internet say they will last for about 100.000 rewrites, that would mean such flashdrives last 2 months, which would just fall under warranty.