A follow-up to our Hermitage experience:
Yes, our US Univ. student was free. She only had her ID card issued by her university, not an ISIC card. The ticket agent didn't seem too happy about seeing the univ. ID but accepted it and didn't say anything.

We bought our tickets online. Like the other poster said, it was still a pretty lengthy line at the Internet Ticket Office at opening (maybe 15 min). But nothing compared to the standard lines. OMG! You'd spend half the day in that line. There were 2 kiosks next to the Internet ticket office. One was out of order. All-in-all, it was worth it spending extra to have the tickets ahead of time.

The Hermitage itself was awesome, of course. But so amazingly crowded (we were there on a Sunday). The Greek & Roman statue area was mercifully uncrowded, but the rest was completely full. Worse than the Louvre on its free-admission day.

Also, it turned out that our hotel (Ren. Baltic) has a special relationship with the Hermitage that lets you skip to the group entrance, if we didn't have tix bought online ahead. So that may be another option.

On a line-related note: We also went to the Peterhof, which was also awesome. But we didn't have tickets bought ahead of time. So we had to wait in the palace ticket line, which took an hour, starting about about 4:30 p.m. The palace was jam-packed with Russian-language tour groups, but we were just on our own.

We wouldn't have minded the one hour ticket line so much, but we arrived by boat and had already had to wait in the lower-garden ticket line for our tickets to that. They couldn't sell both garden and palace tickets from one ticket booth. We took the hydrofoil boats and do be aware, that if you take the boats, you *have* to buy the lower garden tickets (500 rubles). The hydrofoils were a pretty simple way to get there, if not the cheapest (700 rubles one-way, slight discount for RT).