My highest level character to date attempted a metamagick'd (in name, not in mechanics) summon familiar spell late in her career as she'd never had one and had need of something.
She ended up summoning a dread raven (she's somewhat of a dark character). The dread raven had been ousted as the alpha of his murder of ravens and wanted my character to instruct it.
I had little time for this and mainly just had him spy for me.
Towards the end of the game we were tempted by a deck of many things. After surviving my single draw I was content to encourage everyone else to leave when my familiar announced it was taking 4 cards!!!
The thing got 4 wishes, TWO keeps, 100,000 XP, and a bag of gems.
That's how I ended up with a were-dread raven (what he wished he was so he could take on a form people would give more respect) elf, with two keeps, more equipment and almost as high a level as me for a familiar.
Interestingly enough, the other dark-inclined member of the party bargained a favor from the then dread raven for him to wish one of his wishes over to him. Later he found it more expedient to assassinate him away from us than deliver the favor. Sneaky bastard got away with it too.
((See what happens when the DM remembers that familiars are intelligent creatures too and not inventory?))