BY-ELECTION results should come with warnings attached. A few examples to illustrate the point: In 2000 and 2001, Fianna Fáil performed dismally in the two by-elections in Tipperary South, prompting all manner of media analysis about how the party was on the wane. In the following year's general election, the party came within a few hundred votes of an overall majority. In 2006, Fianna Fáil lost two by-elections in Kildare North and Meath. It was returned to power the following year and Catherine Murphy, who won in Kildare North, failed to hold her seat.

The above examples are not made to argue a case that Fianna Fáil can bounce back from its showing in Donegal South-West. That is not going to happen and the party will be doing very well to win 45 seats in the upcoming general election. But the examples do show that by-elections aren't the best yardstick for what will happen in a general election.

By-elections are isolated contests generally won by the candidate who grabs the initiative and builds momentum or who the voters feel is due the seat. General elections are about electing a government.

That said, there are some pointers we can take from Donegal South-West. For Fianna Fáil, there is a glass one-quarter full and a glass three-quarters empty outlook. The three-quarters empty view is that, in one of its strongest constituencies, the party's vote plummeted by almost 60% and if this is close to being replicated across the other 42 constituencies, the party will be lucky to get 30 seats.

The quarter-full view is that, given the by-election took place in the week the IMF/EU formally intervened to rescue the state and allowing for the normal bad performance of governments in by-elections, coming second with 21% of the first-preference vote wasn't as bad as might have been expected. Cold comfort to Brian Cowen, perhaps, but some comfort nonetheless.

Sinn Féin will be cock-a-hoop with Pearse Doherty's performance. It's the first time Sinn Féin has won a by-election since the days Eamon de Valera was its leader. Doherty won't be anywhere near 40% come the general election but he will comfortably hold his seat and it gives a huge boost to the previously stagnant party. If the Adams arrival goes well, the party can also look to win seats in the likes of Donegal North-East, Cork East and perhaps Dublin South-West and Meath West.

There is a temptation to interpret the result as a 'plague on all your houses' approach from the electorate to the main parties. But when Seamus Healy of Workers Unemployed Action Group won a seat in Tipperary South at the height of the boom, similar comments were made and they proved to be ill-founded. At the risk of over-stating the point, by-elections are different. The opinion polls – which have Fine Gael and Labour on a combined 60%+ – do not show that the electorate is moving away from the political mainstream.

However, both opposition parties will be disappointed with their performances. Fine Gael should really have done better as the main opposition party in a time of unprecedented crisis. The result will strengthen the view of those in the party who believe it is underperforming and that Enda Kenny has failed to convince. In normal times, this result might have prompted further mutterings about the leadership but with a general election around the corner, that is not going to happen. Fine Gael will pick up seats in that general election but this result strengthens the argument of those who say its final seat tally will be a lot closer to 60 seats than 70.

Labour's fifth place showing was a lot less than the party expected. In fairness, increasing the party vote to almost 10% in a constituency where Labour has never had a presence is a genuine sign of progress, particularly when Sinn Féin had such a wind behind it.

But Eamon Gilmore has set high standards for his party. It wants to win seats along the western seaboard in the general election and this result suggests it will struggle to do so.

Frank McBrearty may have been an inexperienced candidate but the campaign had Gilmore's identity stamped all over it and it didn't really take hold.

The other slight concern for the party is that, as happened in the local elections, the party came in quite a bit below its standing in the opinion polls. A constituency poll which proved quite accurate in how it called Sinn Féin and Fianna Fáil's vote had Labour at 16%, yet its final result was over a third lower than that. Does that suggest that in opinion polls Labour is attracting high support from people who are less likely to actually cast their vote?

There is absolutely no question that Labour is going to have a brilliant election – almost certainly its best ever. The party will clean up in Dublin and win seats in previously alien territory.

But if Labour is to be alongside Fine Gael in seat numbers, it will have to be in the shakedown for seats in the likes of Mayo, Sligo-North Leitrim and Roscommon-South Leitrim. Even allowing for all the reservations about reading too much into by-election results, Friday suggests that the 'Gilmore for Taoiseach' line is just that, a line.

A lot can happen between now and polling day. But as of now it's hard to see anything other than Enda Kenny becoming the next Taoiseach in a Fine Gael-Labour government with over 100 seats between them.

Unfortunately for them, the economic, fiscal and banking crisis is unlikely to have abated by the time they take power. While it won't stop them putting together a coalition, there are worrying differences between the lines being taken by both parties – not least over whether €6bn or €4.5bn is required in cuts in 2011.

Add in the fact that not far short of half of the new government's deputies are going to be first-time TDs – who will be wholly unprepared for the potential public hostility that awaits them – and it promises to be a short honeymoon for the new coalition.

scoleman@tribune.ie