Western Digital does not recommend installing desktop edition hard drives in an enterprise environment
There they have a point, in an enterprise environment. You don't want your box being down/unresponsive for 2 minutes because one of many disks is doing recovery.
But for home users, the result is the same: after the x seconds with TLER enabled, the device will give up its recovery and report a read failure. The RAID-engine will then kick the drive out of the array. Some try again for a few times (the same sector) but they will still kick the drive out.
On Linux/BSD you can see timeouts happening, and the only issue i ran across was setting disks to spin down to conserve power in a RAID-config would lead to timeouts and disks being kicked out. After setting the timeout value to 60 seconds, this issue disappeared. FreeBSD 8 is also known to automatically increase the timeout of the device when its spun down.
So if you're using Linux or BSD, even a 2 minute recovery time wouldn't be disastrous if you configured it right. It could cause the server to hang when any disk is doing recovery, but for home users getting it to work is more important than 2 minutes downtime. Where enterprise environments use redundancy and would want to swap out any disk as soon as possible whenever the smallest suspicion of malfunction arises.
So, TLER is not a "must-have" in home RAID environments, and may even make otherwise recoverable data irrecoverable, unless you use redundancy like RAID1/3/4/5/6. Either way, having an operating system that allows you to set the timeout to a high value would be more valuable than having TLER, for home users.