My main problem with the new summon monster spells is the sheer lameness of many of the "monsters" such as the celestial badger, fiendish dire rat, etc. These are not "monsters" in the traditional pants-wetting sense, nor do they provoke fear in the hearts of your enemies! The lists seem to be poorly thought out (a natural problem caused by the distinct lack of suitable outsiders of all power levels in the MM). The length of time the creatures remain is too brief to do much good in many cases, and the full round casting time is often too dangerous to undertake in combat situations.
"What? The mage is still casting a spell? Must be a nasty one! OK, I shoot her with my magic missiles! Cool; she blew her concentration check!"
I'm of the mind to create suitable demons, devils, elementals, angels, etc., to use rather than the PHB list. I also think increasing the duration of the creature to 3 rounds + caster level would be a good idea (it's long enough to get some use out of the critter). Maybe even 1 minute/level if the creature is summoned for non-combat purposes (and is unable to attack/defend, but is dismissed upon any successful hit).