Week and a half in Budapest?

Sarah - there is a ton of history. E.g., you could easily spend almost a full day taking in the House of Terror. It's a great walking city, there is much to see. With that much time you can easily get out into the neighborhoods and the hill areas. Don't forget a couple daytrips up the river. Although you do not mention it, the Opera will be going every night, and there are other events.
And don't forget the baths.

Loved Budapest. I think a week would be great. As mentioned above, be sure to include the baths. The opera is a great experience even if you aren't regularly a fan. Compared to other places the quality of the performance is very high and the price very reasonable. You can reserve online. The baths are just off one of the subway lines along with the city zoo. Very easy to navigate.

A week sounds great, because it will give you a chance to relax. More than that might be too much, because compared to many other European capitals the sights are thin. (That said, Budapest is one of the most purely fun cities to visit.). We were in Budapest for five nights earlier this year. We did a day trip to Eger, which was nice. On our way to Czech Republic we stayed overnight in Sopron, which was great. Consider breaking up your stay in Budapest, or doing day trips. We ended up having three full days, because it was our point of arrival and we spent one day on the day trip to Eger. We would have liked more time, but only because it's such a fun place, not because we did not have time to see the big sights. It's a great luxury to have an extended stay in a city, make sure to make the most of it!

Budapest is a nice city but I would split your time with either Prague or Vienna. Prague would be my first choice. You can easily train between the two cities.

Seems like a long time in Buda. I agree Prague or Vienna deserve a look. Or just Prague.

A week plus in Budapest might be a bit too long. I agree that a day trip to one or two of the river towns would be interesting, also maybe an overnight to Eger and the wine caves of the Valley of Beautiful Women would add to the flavor of your visit.

A agree that, while Budapest is great, 7-10 days could be pushing it. I think ten days split between Prague and Budapest would be ideal and fantastic. Check out the Rick Steves itinerary for the Prague-Budapest trip (under tours) for sightseeing ideas) House of Terror is very interesting, a evening Danube river cruise is a must, the bath houses (especially ones frequented by locals) are grand. For culture -- the Hungarian State Opera House is gorgeous, very professional, and priced quite reasonably compared to other great European Opera Houses.

Scrap what I just said. After re-reading Jim's post, I would just spend ten days in the "Valley of Beautiful Women". But that may not interest you so much... Ross in Denver

That is a long time in Budapest. I enjoyed the House of Terror and Monument Park along with the "standard" sights. Eger is fun. I would also consider Budapest-Eger-Krakow.

I enjoyed Budapest so much I returned for a repeat visit. The Opera house tour was great and we attended Der Meistersinger great seats with a very affordable price. There is a lot to see in this beautiful city.

Thanks everyone, for the input! At this point, I'm thinking I might spend 6 days in Budapest and then head on to Vienna for 6 days or so. I'd like to stay a little bit longer in both places, but I've got a deadline to meet a friend in Ireland :)

Sarah-
I would take a day out of those 12 and spend it in Bratislava. It's only about an hour train ride from Vienna and while it doesn't have the sights of the other two, the Old Town area is charming and worth a short afternoon of strolling.