In a word, no. While the media has emphasized United Russia's losses (here and here, for example), the "setback" is only in relative terms. Most political parties would be satisfied with a loss that gave them a majority in the legislative body (after seats are distributed, UR will have more than 50%, even if it does not quite pass the 50% mark in votes). UR will be able to gain legislative support from at least two of the other parties for policy initiatives. Yes, "deliberations" are likely to occur as part of the legislative process, but Just Russia and the LDPR are likely to fall in line when it matters. Just Russia is technically an independent party, but it was Kremlin-spawned and will be supportive. The LDPR's first electoral success was as the repository for protest votes and its leader is known for appearing to be a populist who challenges authorities (see especially Zhirinovskiy's clashes with the CEC back in 1999). The LDPR will also comply when needed.
The only "real" opposition is the Communist Party and its gains are likely due to its status as the new repository for protest votes. Its gains are unlikely to presage a Communist resurgence, however. Having an opposition party that favors state solutions (rather than a rightist opposition) also plays to the Kremlin's advantage .
The response to electoral loss is likely to take several forms:
1) Lobnoye Mesto will be in business as Prime Minister Putin can use the results as justification to make heads roll in the party. The job will fall to Medvedev, assuming that he does not take the blame.
2) Populist policies are likely to be pushed through parliament in the coming months, providing some short-term economic relief through enhancements to pensions, social welfare, housing, or other needs. Putin will spearhead some measures to shore up support in advance of the presidential election.
3) Evidence that the "people's dissatisfaction" is being heard at the top may also come through additional attention to corruption (and another opportunity to clean house like 1) above).
In short, while UR's seat total dropped, and this outcome is likely a direct reflection of public dissatisfaction, political elites still have many opportunities to make policy with limited compromise. Indeed, the loss provides cover for changes to elite cadres that could benefit former and future President Putin.