<p>If I want to put a form up on SharePoint, is it easier to use InfoPath or build a custom web part in C#?  Are there other options that I should consider?  </p>

<p>What are the requirements and hurdles for each option?</p>

Can you be more specific about the form and sharepoint version ?
It depends on your version of Sharepoint : if you got 2003, if you want to use InfoPath, it has to be installed on the clients as well. On SharePoint 2007, i
think
it is not required.
If it is a large form with few business rule, InfoPath can be the way to go -> wysiwyg, and easy deployment.
If your form involves more business rules, a web part or a page in _layouts can be "simpler" and more maintainable.