I like to follow standards and use table-less div based layouts. However using tables to align form fields/textareas and submit buttons is so much easier than using anything else. So is it acceptable from a strict standard perspective?
I see Google, Facebook among others use tables in their registration pages.
Tables can ease the burden in certain forms. I find pure CSS great for single-column forms, however often times I'm dealing with very complex forms with multiple columns and/or require notes, hints, indicators that make using just CSS difficult. For most forms however, pure CSS is the best route to go.
Here's a great getting started with CSS forms tutorial: