When a player plays a very complicated character, such as an artificer or (say) a bard/druid/green whisperer/sublime chord/arcane hierophant, this can impose extra work on the poor DM who has to understand how everyone's characters work. Assuming that the DM is fundamentally willing to deal with this complexity and that the character isn't otherwise problematic (e.g. overpowered), that DM might still appreciate the player going the extra mile to keep the complexity from getting out of hand.
Some things are obvious: if you are playing such a "snowflake", then you should make sure that you know your character front to back; the game should never be waiting on you to figure something out. Another thing is flexibility: when the rules pile up, the DM may need to handwave to keep things moving along.
Having a sort of DM-oriented mechanical summary might help. If you're playing a barbarian of a certain level, the DM will probably have an intuitive sense of what the character can do. A half-page or so outlining key capabilities might be helpful.
One idea that occurred to me, inspired by various LARPs, was to pair mechanical complexity with metagame requirements. For instance, playing an obscure bloodline or using a rare discipline might require that you submit a longer backstory. In D&D 3.5, there are plenty of things that might trigger such requirements, such as prolific multiclassing or uncommon subsystems (e.g. psionics). This could also be used as a worldbuilding tool for a non-standard setting: if you take an ability with a regional requirement, you must write a brief description of the region you come from that provides context for that ability.
I'm looking for ideas from players and DMs, but particularly from DMs who have had players bring convoluted characters. What went well, and what went badly? How could that player have made your job easier?