That Joel Spolsky response was excellent and covers pretty much all the bases. Ideally in any partnership, you will each bring equal levels of effort, energy, skills and focus to the table to warrant an equal split. If the scales are tipped too far in one direction, I think that is a possible source of conflict down the road - especially if shares are split equally but responsibilities are not.
Another key thing to work out up front is how to split up if one of you decides things aren’t working out. The vesting of options is good advice to help there since each founder will slowly gain their shares over time. Standard partnership agreements typically have a mediation clause and valuation clause to help as well.
I also have a friend who added a “Shotgun clause” for his company which basically says something like “Any partner can make an offer to buy out the other partner(s) at a specified price. The other partner(s) must either accept the offer or purchase the other partner(s) shares at the same valuation”.
Hopefully you won’t need any of that advice, but best to work out these details at the beginning.