The main problem with custom firmware (among many other things) is that SCE is going to continue to release future firmware updates, many of which will include features the typical user will want to use.
Granted, the last firmware was easily the worst ever released since it only removed Linux support, but there will be no end to updates until SCE ceases support of the hardware platform.
Put simply, you'll have to rely upon a custom firmware release EVERY TIME a new official firmware release is required for the sole purpose of keeping Linux on your PS3.
To a very select few who either really want to use Linux to fool around with, or because they made the unfortunate decision to rely upon running Linux on their PS3 for media hub purposes or whatever, it will be worth the continual inconvenience, assuming a custom firmware is released to coincide with every official update.
But for everyone else, why even bother? The custom firmware will only keep Linux on your PS3 for as long as it takes for SCE to issue the next required firmware update, which could be in 2-3 months, maybe even less. You'll be offline waiting for a custom update every time this happens.
If someone really wants to make it that much of an issue, and they actually use PSN on a regular basis for gaming, the solution is bite the bullet and buy another PS3 if they insist on running Linux on your Fat because "I have to" or because "I paid for it" or whatever reason you can come up with.
As for offline use, I've still yet to run into a game that won't play on the old Linux supported firmware. So you always have option C.