You need to prove Good Moral character for the requisite three years as the spouse of US citizen. If you have had no problems since then, you should be ok. Make sure you apply after three years have passed from your conviction and be sure to disclose this whether or not you have it "expunged" from your record. In San Francisco the interview should be scheduled within 2 1/2 to 3 months of the date you apply.
Samuel Ouya Maina, Esq. 415.391.6612 firstname.lastname@example.org Law Offices of S. Ouya Maina, PC 332 Pine Street, Suite 707 San Francisco, CA 94104
If your record has been clean since then, it is unlikely you will be denied citizenship. I definately advocate using a lawyer. Even if expunged you have to disclose the offense for citizenship purposes.
Getting your record expunged does not stop USCIS from finding out about your DUI, and it could still affect your case. You should definitely consult with a reputable Immigration attorney in your area. He/She will need to evaluate your case to figure out what your options are. If it turns out that you can apply for citizenship, the application normally takes 6-8 months.
[This answer is for general purposes only; it does not constitute advice and does not establish an attorney-client relationship.]
While I don't practice immigration law, I don't believe it will prevent your citizenship application, although I'm sure you'll have to disclose it. I highly suggest consulting with an immigration attorney. Good luck.